There is often an understanding that a small amount of lateness is acceptable; commonly ten or fifteen minutes in Western cultures. In some cultures, such as Japanese society, or in the military there basically is no allowance.
Some cultures have an unspoken understanding that actual deadlines are different from stated deadlines; for example, it may be understood in a particular culture that people will turn up an hour later than advertised. In this case, since everyone understands that a 9am meeting will actually start around 10am, no-one is inconvenienced when everyone turns up at 10am.
In cultures which value punctuality, being late is tantamount to showing disrespect for another's time and may be considered insulting. In such cases, punctuality may be enforced by social penalties, for example by excluding low-status latecomers from meetings entirely.