Yes. You don't need to take each test on the exact four-month mark.
The one requirement is that all three tests are completed within a single active subscription year. Within that year there is room to fit them in around your life, so if something gets in the way you can push a booking back and take it when it suits you.
Tests don't carry over. Any test not taken within your active subscription year is lost rather than rolled into the next one, so it's worth keeping an eye on the time you have left.
Spacing your tests a reasonable distance apart gives the clearest read on how your habits are shifting your biology over time.