Sometimes its easy to think that you need an hour is a minimum for what you need to get an effective workout... but guess what you can utitlize whatever time you have to get that workout in. Say you have twenty minutes from start to finish.
Here is an example. 5 minute warmup- dynamic movements (jumping jacks/high knees/ buttkicks)
move to a 15 minute Strength Section-
Supersets: 2-3 Sets of 8-12 of a Squat and a Hinging Exercise
2- 3 sets of 8-12 push and pull
2-3 sets of a cardio and abdominal exercise
5 minute quick stretch and cool down.
Make the time- even the short workouts have benefits!