There are two aspects: how long do you have and how much do you want?
Now if the date is a “drop-dead” date then you can make it fit… Well that is, you can make something fit in the time by chopping the end off and saying “Now it’s complete because it ends there!”.
Then there is the “traditional” way of just overrunning until it is all done.
So what do you do if all the features are required AND the deadline is a “hard” one; for instance, the law is changing on the 1st April and if you aren’t ready then, well, someone is going to jail. Well, two things: make sure you aren’t going to be the one going to jail and secondly: you need to find a way to meet the features fit in the time box.
So, what do you do? Fake it, of course! Not really fake it, no point in just having a picture of the application… but don’t have time to write the GUI to input the data? Fine; just use a spreadsheet and some SQL. Don’t have time to validate the data validation framework? Check it manually. It needs to look like a real application of course; the concept is: strapped chicken, it does work, just only under certain circumstances. It won’t last, but then it doesn’t have to… As soon as you get past the deadline you have a whole other quarter to implement the real features.