Ptrost, are you RA or USAR?
lfoosutnd, you are USAR, and I've been arguing with my command about this issue for a while. Allow me to introduce you to the big green weenie:
The 3x5 contracts executed in 2009 didn't contain any of the language indicating an effective date. While the policy is for the 3 years to begin after you complete IET, no mention of this is made on your contract or any references made therein (not that I have found anyway).
They are basing this off of a 2005 implementation guidance memo from HRC to TPU commands which is also not mentioned in your contract. In 2005, the reserve annex of your contract would have actually specified this policy.
My reasoning that such a memo not referenced in the contract could not affect a service obligation has been repeatedly dismissed outright.
Your option for getting paid on this contract involves non-traditional channels and your odds are probably slim at best. You might try JAG or your congress critter, but I doubt they will be willing to take it past an initial inquiry (such inquiries I imagine would go to my command, who would produce the memo thereby satisfying the inquirer; at least that's how my last congressional went).
Alternatively, you can request through command channels that your reenlistment be voided since it was executed outside of your window. I believe G-1 should be the approving authority. Your career counselor will be able to assist you on this.
Regrettably, this will not result in bonus payment unless you reenlist again. Chances are with the changes on 1 June, your bonus amount went down (in some cases a $6k difference)
None of these solutions will result in timely payment. I think you're looking at about a year (3 years from graduation of AIT) before you see any of it.
I'm making a few qualified assumptions here; I would need to see your initial contract to be certain.
To the initial question: no such thing as a bonus advance.
This is a ten level task