Do you have "Full charge has priority" selected in the charge timer menu? If so the car will ignore the charge start time and calculate when it needs to start charging. Mine is set up with a 6:00AM start time and 7:00AM end time with Full charge has priority selected. Depending on the state of charge it will usually start between 1:00AM and 3:00AM.
I have run into some problems with this method though. It seems the car uses your last charge stats to calculate when to start. I sometimes use a public L2 charger that puts out under 5kW. When I plug in at home after one of these sessions the car calculates the start time based on a 3.6kW charge rate rather than 6.6kW and starts the charge between 8:00PM and 11:00PM the day before. My solution has been to let it charge for a few minutes so it knows the current charge rate, unplug it and plug it back in. The timer then starts the charge at the correct time.
2018 Leaf SL, 43,577 km, SOH - 92.16%, Hx - 119.23, AHr - 106.39
2020 Model 3 Performance, 9,581 km