Maths tutes- like otheres mentioned, pick them so you have a break before to study for tests. I suspect you may be doing the maths for life sciences, I'm not sure how they operate.
Bio labs - doesn't really matter. Early on in the week is usually better, get it over and done with
Chem labs - in first year, you often need to submit lab reports. If your lab is Monday, Tuesday or Wednesday, you will need to submit your lab report by Wednesday, Thursday or Friday 5pm (respectively)- which means you have to finish it quickly and perhaps even travel to hand it in. If your lab is Thursday or Friday, you will have the weekend to complete the lab report.
Hope that helps.
As for lecture times, I wouldn't worry too much about them. See
www.timetable.unsw.edu.au