I feel like you’re looking at the wrong place.
The memory management in the Project menu is meant for you to say how you want your OT to deal with its internal memory, sampling vs. flex samples playing.
But it’s not here that you specify the length of one particular sampling session…
For sampling, you will most likely want to specify a number of bars instead of a period of time.
This is done in the configuration of the recording track (Fn + A red button, and Fn + B)
Here you can set the “RLEN” to e.g. 16 steps, or 64. “MAX” default value will allow you to record up to the max value setup in the Project menu…