Consider using the Epic Heroism rest variant
Make short rests shorter.
(Disclaimer: My answer primarily handles the generic question you present. Its applicability to the particular one-shot you are running is not considered.)
In the Dungeon Master's Guide, page 267, are some optional rules which provide a variation on the typical resting rules. This would ...
There are no in-game time constraints
Read it again. Nowhere does it mention any in-game time limits. Indeed it explicitly says the players “have “four hours until planar midnight,” which sidesteps the issue of game time passing differently than real time.”
So they can take as many short (or long) rests subject to the DM’s rulings and the time it takes to ...