I've done the battle sim days at anzio.
The jist of the day is that once the brief safety brief is done then the scenario which the objectives are based around is given and then objectives through out the day are posted via a teams HQ, although it's not always the respawn points as these are often located elsewhere, and as such can be used as objectives/taken and held etc.
In terms of the day. Once it starts it doesn't stop for breaks or lunch, so it's up to you to eat/drink in the game area or return to the safe zone. I've found it a better day when teams have taken breaks in the field and have a drink/take break within the game area, so are never out of play but obviously that's down to the players on the day.
I've played those days as both dmr and aggressive bolt action support (snipe but not Bush wookie) as well as assault/cqb and it works well either way for me bt I would say to wear a watch or have the ability to know the time with you. Objectives are often time based, eg your have x time until x happens or to capture a point. Which I felt was a great idea to stop things getting too stick if one team players decide to take an hour off for lunch.