While you can set a pre-determined length for an individual clip in its settings, it is more typical (and easier) to use the Master Length setting and the Count In/Count Out settings. Recording Count-In determines when recording starts. Recording Count-Out determines when recording stops. Auto Count-Out determines whether the count-out begins automatically when recording starts or if the count-out waits for you to trigger it.
These can be set globally for all clips or made local to a color or individual clip. The text in the settings dialog is helpful for understanding recording quantization.
If you find changing the master length with the popup inconvenient. It is quick and easy to add buttons to your layout or set up MIDI actions to do it.
Usually, the master cycle length is set automatically when you record the first loop. Changing the master (cycle) length is handled in the tempo/clock popup as shown below.
When you tap to start or stop recording, the recording starts or stops at a time determined by the following settings: