I often do rides limited to 60 min. Most of my training is JRA, just riding along, so I do whatever I feel like. I can make that flat loop very very hard if I want to, or it can be really easy.

I do a "Quarry Road Loop" around here, a flat 16 mile loop (350 feet climbing according to Strava). It takes me from 45 minutes to over an hour to do it.

Usually if I'm really time limited I do the trainer. Any time of day, any weather, it's still shorts, jersey, cap, turn on the fan. If I'm cold I may wear knickers, LS jersey, wind vest to keep torso warm, etc. I'm fortunate that I can ride my trainer at whatever hour without disturbing anyone.