I feel that end of day is more variable than start of day, especially if end of day means "Go Home!". Some people have kids to pick up from school/day care and

I feel that end of day is more variable than start of day, especially if end of day means "Go Home!". Some people have kids to pick up from school/day care and leave at 3, while others like to come in later and/or take a long lunch and work until 6-7. Saying everybody must be in by 9.30 is probably easier to coordinate that saying everybody must stay until 5 and then go home at 5.15.