I'm running charger firmware 4.12.3.EU1 and WiFi firmware 2.7.4.
I've been having issues for a while now with the charging failing to stop at the specified stop time. It normally set the timer through the WiFi web page.
When playing around with the timer (through the WiFi) I've noticed that if I set the stop time to sometime in the future and put start time to now or in the past 59 minutes it won't start. However when I put the start time one hour or more in the past then it immediately starts.
In the same way, if I put the start time, say, two hours in the past and the end time more than one hour in the past it won't start but if I now set the end time to less than one hour in the past then the charger immediately starts. Again, whatever way I set the timer it fails to stop the charge.
I'm living in Ireland where the current time is GMT +1 due to daylight savings time.
It looks like your issue was addressed and fixed in 4.13.0.EU. The latest version of EU specific firmware is 5.0.0. Here are the EU releases and notes: