If you are looking for defined abs you can work out every day and 7min's is not excessive ,you don't need breaks when working only with body weight

,remember though less is more , as in the movements should be done slowly and precise ,going fast you can use momentum rather than muscle stength . Also a lot of people use their hip-flexors or neck muscles .
If you want to build bulk as in a " six pack" you will need to add resistance and work out every other day along with good quality food , though a lot is down to genetics.