The short version: Registrations were crazy.
At first only the Chemistry was there saying you could register for it online, then 10 mins before registrations were to open Biology came up but Physics didn't. They'd messed up classing it as a 'non-enrollment activity' meaning it was located elsewhere and I only found it by chance.
I reloaded the site at midday at the registrations didn't open, so I kept refreshing and they still weren't opening, so I refreshed one final time and it took 10 mins to load, so that when I got into my Chem lab registration page I freaked because all but 6 lab spaces were taken and they were all for terrible lab time so I rushed to get a space in the lab with the least terrible time and I ended up with 6-9pm on a Tuesday, which meant that with other things already set on my timetable I'd be having 7 hours straight of Uni, not seven hours at Uni but 7 hours of non-stop science.
Physics (once I found where it was hiding) did not make me happy. The really great lab time I had last semester wasn't being offered so I'd chosen the best of the other labs from the final version of the timetable, however when I got to the registrations page that time wasn't listed, so I had to redo my whole timetable to fit in one of the other lab times, which meant changing around my biology lab and Physics tutorial. There were other problems as well: normal phys labs run weeks 5-10 but there's computer labs in 2 and 3 and I couldn't register the same time for both because the the registration software only pays attention to the day and time of the labs not what weeks they're on so it kept telling me it was clashing despite the labs being different weeks. So I had to mess around more with my timetable in order to find a space where I could fit any of the other 3hr computer labs.
Biology was pretty painless, all the labs were there with the same times as listed on the timetable and reasonable numbers of vacancies in all but the most popular lab time, it was a real relief compared to the other two.
So after all freaking out and the mad timetable changing my timetable was a mess. So I was loading up all the pages to see it I could somehow rework/neaten the whole thing, using labs that still had open spots, when I noticed that the chem labs weren't all filled anymore. Apparently they'd messed up the number of lab spots, listing that there were 10 spots each when they should have been listing 35 spots, so I quickly registered for the lab I wanted because it was filling up fast.
This really improved my timetable, and after changing my physics tute to a better time my timetable's now pretty good. It's nowhere near as good as it could have been if they'd actually had the physics lab I'd planned to choose, but much better than it was when I had the shoddy Chem lab.
This isn't the first time this sort of drama has happened either, every time I've ever had to register for anything using the uni's online system there have been problems: labs timetabled but not available to register for, problems with lab numbers, problems with supposed 'conflicts', and one time that it would proceed, until you'd registered for every lab time meaning that the whole things had to be reset and you had to register for everything again. If it ends up hating you and you have to see course coordinators about things they're really great and helpful and usually get you into the labs times that you need but it's just that the computer system they use is really shoddy.