I’m of the opinion that it’s always better to overestimate something rather than underestimating it or estimating it accurately. If something takes 20 minutes and you are given a couple of days you have multiple options.

1. Get it done asap and early, if you get it done earlier than the deadline then people are happy.
2. If something critical pops up, you can take care of that first then hop on to the twenty minute task because you gave yourself room.

Management loves when things are done early, expects things to be done on time, and gets angry when there’s a delay (and no warning of the delay), so it’s the smart choice in my view.