I think the plan is the banks use these 90 days to sell their less liquid assets that aren't as effected by the interest rate increase. In the end, even being insolvent isn't actually a death knell for banks as long as depositors believe the money will be paid back, which is why the government is putting so much effort into reassuring that 0 deposits will be lost.

Also half the money was literally just to pay back SVB and signature deposits while they unwind their book. Once everything is sold the other FDIC member banks will have to pony up any extra cash to pay the loans back.