to only leave yourself just enough time to do something.
Only allowing half an hour to get from the station to the airport is cutting it fine, isn't it?
cut it fine
To have a very narrow margin for error or deviation. Having only $20 in your bank account is cutting it fine, if you ask me.
cut it fine
Do something closely with a very slight margin, as in Tom always cut it fine, arriving at the last minute. This term uses fine in the sense of "narrow." [Late 1800s]
cut it (or things) fine
allow a very small margin of something, usually time.
cut it/things ˈfine
allow only just enough time to do something: Your train leaves in twenty minutes and you’re still here! You’re cutting it a bit fine, aren’t you?