Use of the track?

[AndrewHiggins]

I'm doing 10x800m reps at the mo' for my marathon training and have thought about doing them at the track but:

a) can you just turn up on a Tuesday session and do your own thing?
b) can I use the track at other times? My training plan has these runs on a Wed. Now I could rearrange to do on a Tuesday if necessary but I'd prefer to do them on Wed. Obviously the club house won't be open but can I just turn up and use the track?
c) how fast are the Tuesday people? I don't mind being the slowest but not by a mile!
d) I know the track has all manner of marks on it but is each 100m marked so I can check progress vs target on the way round?