My husband and I did the workouts as an adjunct to our other stuff we do. I never did 90 days in a row!! so I am probably not the one you want to talk to..
I found I did get stronger and it did force me to do some workouts that I otherwise would have avoided...overall I really liked the program and I am sure I will pick it up again -right now I tend to just do the "core synergy" as it covers all the major muscle groups in one session.
Good Luck
(and there is no shame in taking a day in between when you are first starting- depending on your fitness level when you start- you may find it a bit overwhelming- I know I did and I started out thinking I was reasonably fit!!)