No, the typical differences are about 15 minute jumps. In your example, if you must have more than 30 mins, and 45 is too long, just run the 45 and end the workout when you want. When in doubt, pick a slightly longer version and just quit when you are done.
You can use the “not enough time” answer at the completion of the workout to handle it with AT and it should give a normal Intensity survey at that time, so AT can calculate your PL changes.
I am adding the “feature-request” tag to your topic, so it is sorted and can be filtered easier for reference by TR.
Edit to add: This existing feature request may be more in line with your idea. You can add your thoughts there, or I can even merge it directly if that is your preference.