A smart approach to managing your time is allocating no more than 20 minutes to any task you need to do. So says this: Everything should take 20 minutes | The Outline.
The reasoning in a nutshell:
Think about a task you wish to or must complete, and imagine how long it should take you. If you are a right-thinking person like myself, the answer is “20 minutes.” A 10-minute task is hardly a task at all, more of a minor interruption, and anything that takes 30 minutes invites the thought that you could have watched a half-hour episode of television instead. Twenty minutes is, objectively, the ideal amount of time — the Goldilocks number when it comes to doing things.
Now you can quibble about it, but it’s a smart rule. If you are still unsure, read the piece.