https://www.ssa.gov/OP_Home/cfr20/416/416-0420.htm
> We generally use the amount of your countable income in the second month prior to the current month to determine how much your benefit amount will be for the current month.
Earning $5k in a particular month would mean zero benefit in a subsequent month, and keeping that $5k sitting in their account to tide themselves over would put them over the $2k limit on assets, making them ineligible for SSI.
> The Social Security office may approve your request for reinstatement. If your request is approved, your temporary benefits start the month following the month in which you made your request. Temporary benefits can last up to six months.
So: it’s not instant. It’s not immediate. And it risks losing the benefits altogether if they mistake a one-time contract for something he could sustain indefinitely.