The only issue I have ever had with time zones is when driving alongside the River Danube in Romania. Serbia ,a couple of hundred meters away on the other side of the river, is in a different time zone. The time keeps changing between Romania and Serbia time. Not a fault - it just shows how precisely it normally picks up its signals.
I am also cautious of using a mobile phone ,or phone based navigation system , on that road because if its picked up by a Serbia carrier the cost is MUCH higher than in EU Romania.