Generally speaking, some subjects have two hours worth of lectures and some have three (usually science). In the case of Edmund he's slack and is only doing two subjects (only joking

).
You get to pick your timetable but there are constraints in terms of clashes and so on. Choice usually increases with the number of students in your subject, but some time slots are quite competitive so you have to get in early. For example, there are three Biology lectures for me each week, with the 11.15 time-slot being booked full pretty early. It didn't fuss me, but it fussed others and people started turning up to that session even when it wasn't on their timetable so the lecture theatre was over-crammed and they had to kick people out once they realised what was happening.
Everything shows up on the timetable though, skipping lectures is always an option.