and the shares are yours. You did not borrow, as there are no maximum shares anyway.
You can hold it forever. If it IPO's at 10 and delists 5 years later as a dead project, your short is still your short.
When you short, you are saying that you think the current price is too high and that it will go down. At some point in the future, you cover. If the value went down, you gain the difference less commissionn on the cover. The value is the original cost plus the difference in value times the number of shares. (Note: if you "Buy" and it goes up, the same formula. Price paid plus difference times number of shares)
If the current price has gone up, then the value of of your shares is the original cost LESS the difference in share price times the number of shares. (Similarly, if you "Buy" and the price goes down, your value is the original cost less the difference times the number of shares.)
The tricky thing is that a "long" or "Buy" current value of your holding is simple...current price times number of shares, because you add for gain or subtract for loss from the original cost amount.
But a "short" looks different because the change to total value is reversed.
I know this is long winded, but I am trying to give a full answer. If you have questions, post them.
Shorting is a major part of the game. Lots and Lots of MovieStocks are issued and movies never materialize. Thes are long term shorts, but not a good answer for newbies. But the numerical concept is the same for derivatives, MovieStocks, Funds and StarBonds when you buy/sell or short/cover.