I just got my letter in the mail saying I need to update my income estimate for 2009/2010 financial year, and Im a little confused....

So my son was born end March and we have been receiving the baby bonus and base rate of FTB part A. Im on paid leave at the moment but only for about 9 more weeks. Then I have about 9 months maternity leave unpaid. So when I filled out the forms in March I included an estimate for 2009/2010.....but in the new letter they increased the amount. So now Im trying to work out what to do! Im so confused....I blame baby brain lol.......so this is best I can figure I should do:

For my wage, work out how many weeks pay I will get in July.....but then what about from March - June 2010. I dont know where I will be or what I will be doing then!! I legally have a job to go back to, but Im not sure if thats what I will do....so should I put my "normal" wage from my old job for March - June 2010 just incase??

For DH's wage, I was hoping to get his group certificate for this year before I had to commit to any with the gov for next year....but if I just work out 52 weeks of his current wage, and throw in afew extra for bonus/overtime???

So if I do that, and hubby does get a bonus or two, or if I go back to work earlier, do I just ring them or do something online each time.....or am I committed to the estimate I give now???

I just dont understand if the payments I receive are based on week to week or a yearly average?? I guess what I mean is if I put only a couple of weeks wage for me, then do a couple of months work....if I update centrelink every week will I avoid a debt at tax time??

Thanks heaps to anyone who read this far lol...sorry if that makes no sense what so ever....I just worry about doing the wrong thing and getting in trouble with the Gov lol