Monthly pay is usually much better once you're settled, nearly all your bills, DDs etc work on a monthly basis, it should make life easier for you once you get used to it.
I do temporary work normally, and hate weekly paid contracts in comparison to monthly.
Sounds like the interim payment is a 2 weeks sub, to help you all get through to the first monthly payday.
I'd suggest try have a really tight month first off, and really try get by on the 2 weeks money.
When you get paid on 16th March, (a month, minus the 2 week sub) last as long as you can, then sub another 1 week's worth only if you have to, and try get by.
Also, you won't have a lot spare out of this March payday, so a few days before then would be a good time to make some calls and try re-arrange any DDs you have, so they don't try take any more payments until after 16th April. You can buy yourself a whole month if you're clever about it.
If you can stick to that:
Feb 16th you get a sub of two weeks wages
March 16th you get a month, minus the 2 weeks sub
April 16th you get a month minus the 1 weeks sub, your DDs go out.
May16th you get a full months wages, and you're settled.
Alternatively, If you've a credit card things are even easier, you can use your card to get you through March until the April payday, which will be a full months wages.