Between AM-M, it will depends on the firm situation at that time. Sometimes they will play with a 2yr AM system, or a M0 system.

So you will hit M1 at the start of 6th year, or maybe 7th year. Then you will hit M3 in 8th or 9th year. Promotion between associate to SM is a certainty for most ppl unless your performance is shaky. It is rare but it does happen. Reasons such as making mistakes that piss off clients or managers, or having a fairly obvious lack of ability (usually accounting knowledge) to do work properly