Then your bottle is different from mine, mine says nothing about "as directed by your doctor".
But the last sentence reads.....as directed by doctor or then only as dandruff control....so!!!
1) Use it every 3 - 4 days initially or if you have been given it by a doctor then use it according to his/her directions.
2) When your 8 weeks are up use it once in a while to control dandruff (once every week or so) or continue to use as per the doctors prescription.
You're supposed to use it frequently to begin with to get rid of the dandruff then only use it once in a while to control it.
Seriously though, don't be so pedantic about what it says on the bottle. Just use it every 3-4 days all year around. No harm to be done.