Retention NCOs, where in the regulation could I find this?..

My Career Counselor is stating I must be within 90 days of my DEROS to be slotted into a school for reclass.

Last month I approached him for reclass, met all requirements etc but was told there were no available school dates or seats.

I am currently playing the waiting game since being told there were no available school dates for my MOS. He says once October arrives, the new fiscal year, he will be able to see more open slots such as classes in january and beyond.

My DEROS and ETS are a few months apart so he recommends I extend my DEROS to my ETS so I have more time to get into a school for next year.

I just want to confirm through black and white that due to me being overseas, the regulation says I have to get into a school date 90 days within my Deros. I mentioned TDY and return to him but unfortunately I cannot recall what all he said about that option and that the best thing I shpuld do is wait until October with the same DEROS and ETS.