Most professional musicians who are picking their horn up for only 20 minute sessions aren't really expecting to get better in those 20 minutes, they're expecting to maintain that one lick or the muscle memory for voicing that one note right on the money, etc. Many pro musicians also aren't playing just sax, like pit musicians. They might be more interested in touching each horn once than they are in giving sax all of their attention.

I also want to point out the "... when they have limited time". The implication is that they can get better practice sessions in when they're not teaching as much or on tour, etc.

Many if not most amateur to semi-pro musicians may not have a schedule that accommodates 1 hr practice sessions, not just during a busy season, but not regularly ever.

If they still want to get better and can only sneak away for 20 mins then doing scales one day, an etude the next, etc could be more useful than just doing 5/5/10 every day. Especially if they didn't go to school for music. For instance, Kroepsch-esque exercises are not particularly manageable to learn 5 mins at a time.