Yeah alright, would it be a good idea to have different tabs open for each unit, and then qucikly switch and click when the time comes?go on about 10 minutes before hand. If you dont get your times, you can always put in an application (which is bullshit so i dont reccommend this), or you can talk directly to the school and theyll fix it for you with some "PERSUASION". It was hell getting to get them change my times when I called them up! They made it super hard for me to talk to the lady on reception who was the one with authority to change classes etc. I had a good reason to change though!
EDIT: you should be fine if you go on about 10 minutes early...dont keep on refreshing the page every 5 seconds. just refresh it once it hits the time or like a few seconds before it hits the time. All the best of luck with your tute registration. And remember, click quick! because others are waiting staring at the clock exactly like you are.