Here’s a neat, fast, flexible workout: It’s called Guerilla Cardio. You can web search about it, but here’s some links.
Long story short, it’s 12 minutes. If you do it right, it feels like a gorilla worked you over.
You can do different kinds of activity for it: wind sprints, kicks, jumping jacks, you name it.
Three parts, essentially. 1) Four minutes at half speed. 2) Four minutes of going at full blast for 20 seconds, resting for ten seconds, repeat. 3) Four minutes at half speed. Then done.
If you do the half speed part right, you can use the time stretching.
Here’s a more detailed breakdown:
Here’s full details, an article that’s like 10 pages:
http://www.morandosozinho.net/bar/wp-content/uploads/2008/03/guerillacardio1.pdf
The trick to doing it is this: It’s impossible to time :20 on, :10 off. So in my experience, the best way to regulate it is to assemble some kind of audio track that has snippets of music that run for the allotted time. So you have four minutes of midtempo, 20 seconds of superfast, ten seconds of slow, etc.
Which is pain, but if you know someone who’s done it, they’ll probably be happy to share.