When relief comes stay in brake room or chill in my car??

Hello if I am scheduled to work 6:30 to 7 but my relief comes in at 6:30 I see many techs and nurses and pcas go to brake room for the last 30 mins. If I am a tech can I just chill in my car for the last 30 mins and clock out from there or do I need to stay in brake room?

Again I see some staff take off and some stay in brake room so I want to know if it’s optional or there is a requirement??