Is it appropriate to not compare all samples and rather 2 of them and another 2?

#1
I’m preparing within a group repeated measures study with duration of 3 weeks.
1st week - no technique is applied, it’s a control group, 2nd week - a technique A is applied, 3rd week - no technique is applied. Measurements are taken several times per day.

H0: frequency of performing an exercise doesn’t depend on technique A.

It's been told that while having more than 2 groups it's not a good way to compare each pair of groups separately. In the current study, I think to compare 1st & 2nd weeks and then 1st & 3rd weeks to see is there a difference. Will it be right to do?

Thank you in advance for suggestions!