A short rest is at least 1 hour long in 5e, if playing by the standard rules. If you’re playing with the Epic Heroism variant rule, a short rest must be at least 5 minutes. If you’re playing with the Gritty Realism variant rule, a short rest must be at least 8 hours.
Player’s Handbook, page 186; Dungeon Master’s Guide, page 267
The benefits of taking a short rest include:
The option to use Hit Dice to restore hit points
The ability to recharge class and subclass features, as well as feats and magic items
If a short rest is interrupted before completed, you do not gain any benefits — regardless of the short rest rules you’re using.
The Dungeon Master’s Guide suggests two short rests per day (pg. 84), but this is not a hard-and-fast rule.