Originally Posted by Laurel:
But, be warned. Before I started this they were getting here late like at 5:35 or 5:40. So now that they pay for a half hour they get here at 5:55 to 5:59. Funny how they could make it here by 5:40 before but now don't make it till about 6:00, sometimes on the dot. 
Occasionally (very occasionally) they come at 3:30 though and still pay the same so that is cool.
Laurel
THAT ^^^^^ is exactly why I suggested doing it in 15 minute intervals and then charging your late fee after 15 minutes.
Seems people will stretch every bit of time you allow so giving too big of a chunk of time will probably backfire like Laurel said happened to her.