My take:
Weekly, weekly, weekly, weekly!
I stress: weekly.
A beginner left on his own for too long will use all his practice time on programming the fingers (read: brain) to do wrong things. It then takes a lot of time again to make the wrong right. It's counterindicated in every discipline I know of.
In paddling, for example, this has been quantified to be that it if it takes one week to learn a thing correctly, then it will take six weeks to correct a learnt-in incorrect technique - totalling to seven weeks of work where one week would have been enough.
Fortnightly or even less often is for medium (maybe) or advanced students
IME, no student of mine who demanded lessons once a fortnight actually became a good player. It has always been a case of "something else is more important, always", and they would never practise daily.
So I just stopped offering that option at all.
Oh, and I myself had a teacher once who would only teach every other week, and who also often couldn't make it. I stalled totally in the beginning, and then fired him after a few months, and found I learned more from myself by taking that responsibility than what he taught me.
Other than that, in 20-25 years of getting taught, I always had teachers who didn't even discuss the matter, and taught once a week. I'm grateful for that.
best,
bert