I only do the 7 minute exercise, is that enough?

For now, I have sticked with the the 7-minute workout, but I've been thinking to add the 5-min abs-core workout this week.

Go at your own pace. Do you know your body well enough to push yourself to 10 minutes without feeling as though you have exerted yourself? I say up the ante on your workouts (how much time you spend working out) and see how much you can handle. If you find that you can't handle many minutes spent working out then decrease how much time that you do spend working out. Find out what works best for you & go from there. Remember that it's not about how much time you spend exercising it's that you are productive in doing it. We're looking for progress, not perfection.

Yea it is! I do that too and as long as you dont sit all day after its fine but only 7 minutes in the whole day is not enough.

Yes it absolutely is! If you only want to do a short workout that’s still a good exercise and you should do what’s comfortable for you! You can also go for walks during the day to incorporate more exercise into your daily routine!