Set your watch back or forward 5 minutes so that when you arrive at 6:30 (according to your watch), it is actually 6:35 for them.
This actually reminds me of high school. Four days of the week, all classes finished/started on a time that was a multiple of 5. But 1 day a week, we had “home room”, which added about 20 minutes. In order to compensate, all the rest of the class times were shifted around so that the final end time for the school day remained unchanged. So, for example, our schedule might be like this M-Th:
First hour - 7:20
Second hour - 8:25
Third hour - 9:30
Fourth hour - 10:35
Lunch - 11:40
Fifth hour - 12:10
Sixth hour - 1:15
School day ends: 2:15
But on Fridays:
First hour - 7:20
Second hour - 8:22
Home room - 9:24
Third hour - 9:42
Fourth hour - 10:44
Lunch - 11:46
Fifth hour - 12:16
Sixth hour - 1:18
School day ends: 2:15