What is the best time intervals between pre test and post test?

What is the best time intervals between pre test and post test? if if you conducted a pretest on the 2nd day of the first week of research, then the post-test can be done on the 2nd day of the 7th week of research. This gives researchers using an interventionist /treatment programme a minimum 6-week period to do their intervention/ treatment .

if if you conducted a pretest on the 2nd day of the first week of research, then the post-test can be done on the 2nd day of the 7th week of research. This gives researchers using an interventionist /treatment programme a minimum 6-week period to do their intervention/ treatment .