I did 5 days in a row of level 1, and then fell off the wagon a bit with a neck crick that didn't allow me to move.
This morning I was lazy so I slept in, but I'll probably do level 1 again tonight, and/or tomorrow morning.
I didn't notice a huge issue not taking days off, the first 2-3 days were rough but then my body adjusted to the whole concept of working your muscles.
I think "officially" you're supposed to do level 1 for 10 days in a row, then level 2 for 10 days, then level 3 for 10 days, with no time off, but honestly, I think if you can fit it in 3-5 times/week you're doing well.