if office timing is 10.30, grace period is 15 minutes so till 10.45 .

if you want to count late coming of an employee thenwhich is late coming 10.31 ot 10.46

Hi,
If you have a grace period of 15 minutes and if your shift start time is 10.30 am then late coming applicable after 10.45 am.
These are all company specific. While you are concerned about their In-time also please check their out time in the previous day - whether they gone late.