The majority of companies I worked for have had a grace period. There is no grace period. You would get a 1/4 of a point for being less than 30 seconds late. Take that as you will, but in my opinion and experience, that is a rather steep consequence for such a small infraction.
There was also a point in time where there were large orders going out, which meant that we had to work overtime, which wasn't the issue. The area where I worked made components for a different location and we had to work mandatory overtime. My area had to work mandatory overtime with no possibility of leaving early, but the area we made parts for did not. And the people in charge would not change their minds even though they gave no valid reason for requiring us to work 50 hour weeks.