I try to look at these questions a bit differently: How long is the video I'm going to produce? Have I done one like this before? What kind of footage did I get, and how easy is it going to be to edit it into a finished, polished film.
Editing is an essentially creative art, rather tnan a mechanical one. Any of us can crank out a lousy video in a few hours. On the other hand, I just spent the better part of a month editing a fifteen-minute documentary. So, the sky is the limit, and in most cases, we're limited by the budget that we've got. If you've got the budget for three days of post-production, than that's how long it's going to take.
What I'm getting around to saying is, I'm not sure you can get a meaningful answer. If you've never done a music video before, it's probably going to take two or three times as long to get a quality result as it would for someone who does a dozen a year.
With all that said, I'd suggest looking at the length of the finished project and figure two days per minute if you've never done this type of project before, and about a day per minute if you have. That's to produce a professional result–you can knock out something of lesser quality in a day.
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