When does the time limit starts?

Hello I am using zoom to give an english class to one student. We are both using free plan so we should stick to the 40 minutes time limit. And I was wondering when does the 40 minutes time limit actually starts? Is it based on the time when the host starts the meeting or when the participants actually enters the meeting that is already opened by the host?

I tend to start the meeting like 4-5 minutes prior before the student enters. So I am concerned I might be wasting the time limit by starting off early.