You can always hedge your shorts and limit your downside. It’s not a huge issue unless you have absolutely no idea what you are doing.
It seems like a prudent warning in a thread explaining the very basics of short selling
Also worth mentioning you might be on the hook to buy it back at any time; after all, the person you borrowed it from may themselves wish to sell it. If widespread, this is the basis of "short squeezes" (e.g. of GameStop fame/infamy), if a lot of short sellers are trying to buy it back at the same time
Spoken like someone who's never actually done it. Hedging to limit max loss is extremely expensive.
Does market closing and not trading continuously affects this?
If market opens at significantly different price, you may be forced to liquidate and loose more than expected.