Can I wait longer than my on-paper ship date to choose an mos contract

My recruiter just told me that the DD and DG contracts are currently full (even though he told me before that there were spots available). I really want to get an intel or cyber job, although my third choice was comms, I am still hesitant to take it.

He keeps telling me that comms can get TS clearance, but I wanted an intel or cyber job to be stationed anywhere and for the experience.

He told me that I can either wait for October to find another DD or DG contract, but I would have to find someone to take my current spot (September 8). Or, he would keep checking if anyone else has dropped a DD or DG contract in the meantime, then reserve it.

I have been in the DEP since April, can I wait longer than the ship date to choose a job? And if so, do I really have to find someone to take my spot for September 8?