Key facts
- Independent hard charging windows overlap; a tariff time band alone does not necessarily control charging.
- The illustrative 01:00–04:30 overlap lasts 3.5 hours and adds 22.05 kWh at assumed 7 kW and 90% efficiency.
- An assumed 28 kWh battery gain needs about 4 hours 27 minutes at the same power and efficiency.
- Location, repetition, time-zone and daylight-saving settings depend on the equipment and service.
If your EV waits all night or charges for less time than expected, check who is controlling the session. The car, charging station and an energy-service app can each hold charging back. With independent hard permission windows, charging can occur only while every necessary controller allows it. A cheap electricity period, by itself, changes the price rather than opening the charger.
Start with the saved settings and session log, not the assumption that the hardware is broken. This guide concerns ordinary scheduling controls. A charger or vehicle displaying an electrical fault needs its manufacturer’s troubleshooting procedure, not more timer changes.
Separate a price window from a permission window
| Setting | What to establish | Common misunderstanding |
|---|---|---|
| Car charging schedule | When the vehicle requests charging, at which location and up to which charge limit | A plugged-in car must be requesting energy now |
| Charger schedule | When the station permits delivery | A car’s request overrides a closed station window |
| Managed-energy service | Which registered device the service controls and when it grants charging slots | Another app can independently enforce a competing timetable |
| Electricity tariff window | When a price applies under the contract | The price timetable necessarily switches charging on or off |
As a documented U.S. example, ChargePoint Home Flex guidance lets users edit start/end times, distinguish weekdays from weekends and correct the selected utility plan. Those settings describe the listed Home Flex models; another charger may organise its controls differently.
Worked midnight example: three schedules leave only 3.5 hours
Assume an ordinary Monday-to-Tuesday night without a daylight-saving change. The vehicle is connected throughout. These invented windows are independent hard gates, with no override or automatic extension:
| Controller or tariff | Start | End |
|---|---|---|
| Car permission | Monday 23:00 | Tuesday 06:00 |
| Charger permission | Tuesday 00:30 | Tuesday 05:30 |
| Third-party control permission | Tuesday 01:00 | Tuesday 04:30 |
| Assumed cheaper tariff | Tuesday 00:00 | Tuesday 05:00 |
The common charging window is 01:00–04:30, or 3.5 hours. It starts when the last required gate opens and ends when the first closes. The car’s seven-hour window does not provide seven hours of charging; the charger’s five-hour window does not provide five either. In this example the entire 3.5 hours also falls inside the cheaper tariff period.
If the third controller were absent, the car/charger overlap would be 00:30–05:30. The final half-hour would fall outside the assumed cheaper period. This illustrates why available charging time and cheap charging time need separate lines in your plan.
Check whether the overlap can deliver the energy you need
Continue the fictional example with 7.0 kW sustained supply-side power and 90% supply-to-battery efficiency, both assumptions. Over 3.5 hours, the supply delivers 24.5 kWh and the assumed stored gain is 7.0 × 3.5 × 0.90 = 22.05 kWh.
If you need 28 kWh added to the battery, the shortfall is 5.95 kWh. At those same assumptions, required time is 28 ÷(7.0 × 0.90) = 4.444…hours, about 4 hours 27 minutes when rounded upward to whole minutes. A larger target in the app cannot make a 3.5-hour hard window deliver that energy.
Resolve the energy requirement and usable window together. Agree a longer permitted period through the intended controller, accept any applicable different-price time, or obtain the energy through another planned session. Do not raise an installation’s electrical limits to compensate for a timer conflict. For shared household capacity, see the overnight energy budget for two EVs.
Choose the controller intentionally
For a simple fixed schedule, make clear which system owns the timetable and set other ordinary charging controls according to its manufacturer’s instructions. Retain the vehicle’s appropriate charge limit and the installation’s safety limits. Record the original settings before changing a timer so you can undo an unsuccessful experiment.
A managed tariff is different from an ordinary timer. In its UK Intelligent Octopus Go FAQ, Octopus asks users to ensure other charging services are not controlling the car and identifies competing vehicle or charger schedules as a possible cause of unexpected charging. Follow the setup for the device actually registered with the service, rather than disabling the service that supplies your intended charging plan.
Solar control creates another reason for a deliberate choice of mode. A tariff-only window may not match a surplus-solar opportunity. Our solar surplus versus export-and-off-peak comparison addresses that cost decision; it does not establish how your charger arbitrates conflicting commands.
“Start at” and “finish by” are different promises
Tesla’s Model 3 scheduling manual distinguishes a start time from an end-by time. It documents location-specific schedules and situations in which charging starts immediately. It also describes combining some schedules within the vehicle. Those rules are why the independent-gate example above should not be treated as every product’s internal scheduling algorithm.
Read the actual label. A finish-by function may calculate a start time; a fixed end may stop a session before the target is reached. Determine whether a target is a final battery percentage or an amount to add. Check whether the schedule repeats weekly, applies once, or applies only at the saved home location.
Midnight, time zones and clock changes
Write an overnight interval as two dated timestamps. “Monday 01:00” occurs before Monday evening, while “Tuesday 01:00” follows it. Interfaces differ in how their weekday selection describes a window crossing midnight, so confirm the next scheduled occurrence shown by the device.
Victron’s EV Charging Station manual documents a selected time-zone region and automatic daylight-saving handling. It also distinguishes enabled schedules from the operating mode needed to run them. These are product-specific settings, not evidence that every charger updates its clock the same way.
Where a clock change occurs, a wall-clock interval can have a different elapsed duration or include a repeated time. Check the vehicle, charger and tariff’s time convention after a clock change or location change. Do not assume a phone’s displayed time proves that a separate charger clock is correct.
A compact diagnostic record
- Record the charge target, current charge and required departure time.
- List every active schedule, saved location, weekday selection and controlling service.
- Write the next start/end timestamps and identify the actual overlap.
- Compare the overlap with a realistic energy/time budget.
- Change one ordinary scheduling setting at a time, following the chosen controller’s instructions.
- Check the next session’s actual start, finish and energy delivered; restore any temporary test setting.
Use your real electricity contract when evaluating cost. The home charging bill guide explains why the energy rate and other bill components require separate checking.
Frequently asked questions
Should I always switch off the schedule in the car?
No. Decide which supported system should control charging and follow its setup. The correct configuration depends on the car, charger and any managed tariff.
Does a cheap tariff period guarantee the car will charge?
No. A price window alone does not resolve a paused vehicle, closed charger window, reached charge limit or conflicting control service.
Why did the car start before my expected cheap period?
Check whether you selected an end-by function, an immediate-charge override, a managed-service slot or the wrong saved schedule. Use the session timestamps to identify what actually happened.
Method: Official sources checked on 12 November 2026. The overlap example assumes independent hard permission windows and a night without a clock change. All worked scenarios are original illustrative examples, not first-hand vehicle tests.