In 5E, short rests take a full hour. That’s long enough to discourage some players and entire groups from relying on them – a real problem, since a number of classes are built around the idea of getting short rests, specifically around 2 short rests per 1 long rest.

We can resolve this by saying that a short rest requires only a few minutes – perhaps 5 or 10 – but also requires the character to spend at least half their maximum Hit Dice (rounded down) on healing. This would allow characters to take 2 short rests per long rest, although there are some breakpoints: at 1st level they can take an unlimited number of short rests (but there aren’t likely to be a lot of possible abuses at that point), and at 3rd level they can take 3 short rests per 1 long. I think that’s less of an issue than short rests which are too long to get used.