Track all time that you work. If you work on weekends or on a train and you're genuinely working, then track it.
Time tracking must be complete. Your holiday allowance and salary are tied to this.
Your time worked must be tracked within 24h of doing the work. No exceptions.
Don't track time spent at lunch.
Some activities have specific time tracking rules. E.g. dinners with customers can be tracked up to x hours, after the proverbial third beer you are on your private time. Find out what these are from the AL: Activity Lead. In case of doubt ask the HoP.
You yourself are responsible for correct tracking. Do a weekly check to ensure that everything is recorded properly.
If in doubt where exactly to track, just ask the AL or HoP.