How does the even/odd thing work? Is it the number the lab end in, so L2 and L4 would be in the same week?

For first year courses anyway (iunno about upper year labs) odd usually indicates the first week, and even usually indicates the second week for EOW labs. Because labs are every other week, there's 2 weeks the same experiment is being run, so you'll either do it week 1 or week 2.

The higher the number, the later in the week your lab is. For example, L01/L02 would be in the Monday at 8:30 timeslot, just for week 1/2. L03/L04 would be in the Monday at 2:30 timeslot, for weeks 1/2 respectively, etc. etc.

its' different for each course
for bio 1A03 - odd labs went the first week
for chem 1A03 - even labs went the first week
so just to be safe, pick a wednesday/thursday lab so even if you are in the first week, you will still have enough time to figure the lab out and ask other people how it went..

for orgo - labs 1-5 were the first week
and 6-10 were the second week...

so it all depends..
you find out in the first week of class which labs are going first

also, the higher the number, doesn't necessarily mean you will be at the end of the week
for chem 1A03 i had lab 48, but I went on Monday's of the first week...

I'm just worried that all my labs will be due the same week! O_O

chem labs were due at the end of the lab
bio 1A03/1M03 were due the next day
except for the formal lab report, which we got a week/2 to do

You can't tell until the first week of class, because even if odd start first and even follow, the first week of labs can vary from one class to another. E.g. one class starts odd labs on the week of Sept 12th while another lab also starts with odd labs but with the week of September 19th. So you can't really tell yet.

Also, some classes skip the week of thanksgiving, others do not. I have started off a term having two labs on opposite weeks but finished with them on the same week, because of this.

Is it bad to have a lab on mondays?

I always try to avoid Monday labs. You don't necessarily know if your section will be the second week of the experiment or not, and if you're in the first week you are the "guinea pigs" for the lab. A lot of the time I found that TA's would have tips for the later lab sections learned from the first lab sections; ways to complete the labs quicker/steps to avoid/changes to lab procedures etc.

Having a later lab gives you the advantage of talking to others who have already done the lab.

PS- Having multiple labs due in one week is not a big deal, really.. I used to have weeks where I'd have 3 labs in the same week. Plus, if they're all due one week, the next week you generally have a lot less work :p