I was eager to be early for my first 1:1 rehearsal, ending up at the shuttle-bus pick-up point by 8:20am for a rehearsal supposed to start at 9am, but needn't have worried, as there was a lot of hanging around waiting for organisers to get sorted and others arrived, so it was about 10am before things properly kicked off.
Definitely agree about taking suncream. I've had sore shoulders all week from the sunburn I got rehearsing on Saturday, and that was a fairly overcast day. Sunglasses recommended as well: face was a bit achy from squinting all day. If you do carry your mobiles etc with you on your person, make sure they are fastened/zipped/buttoned securely: One guy's iphone went flying across the concrete during an exercise, persumably coz he'd just popped it loose in his pocket.
My bib-number was changed when I got there, but I think that was partly coz there'd been a mix-up when I was first allocated it. So yes, bib-number changes can happen.