Short contracts have a deadline, don't they? That makes it hard to act on a vague but overwhelming feeling that the market is going to tank at some point. I suppose it might be reasonable to just sell out, if you really feel that way ... but then you're in dollars! They don't call it "uncertainty" for nothing.
I'm not sure what you mean by that but in general, not really. If you are short a stock there is no time limit. If you are short stock index futures, well yes the contract has a date, but it's not a big deal since you just roll forward to the next period. You might be thinking of options (puts), where yes, they are dated and you are losing time premium while waiting.