I did one time provide a room that slows down time for my players. It was after a highly long dungeon stretch at what was the finale of the campaign.

It helped that the dungeon itself was a time warped anomaly so it was easily justified. The whole place was also modelled after the IRL Titanic.

Afterwards they had to fight a gauntlet of a fake final boss, an escape sequence and then an abomination of a dragon (which before seemed to be the fake final boss's pet) rampaging through a city, before said dragon revealed it's true form as a far realm abomination with time based powers.

Sometimes you gotta allow your players to cheese a little.