Ann I've been doing one of these with a more traditional 10 minute mat, especially one more ab focused. I don't think I could hack two of these back to back!
Ann I completed the complete challenge day by day the first time through. On my second "go round" I'm doing two a day. I'm probably one of the older practitioners on this challenge at 69 and I wouldn't say I am "camera ready" or doing the HIIT exercises nearly as rapidly as Courtney. I am finding that I have a little more verve and have been doing the second non adaptive version more often.