According to two Search Engine Watch moderators, Mikkel and Marcia, it takes less then a week to get indexed and ranking at MSN Search. The small thread is named How Long does it Take for New Site being Indexed to Receiving a Ranking through MSN? Answered by a few folks including;
Mikkel deMib Svendsen: MSN is probably the engine that index and rank new pages the fastest at the moment. At least, thats my experience. I usually get most new sites indexed and well ranked within a matter of days.
Marcia: Yep, less than a week from when the first pages are uploaded. And then they pick up new pages added almost immediately.
Forum discussion at Search Engine Watch Forums.