As others have noted, the waiting periods vary between jurisdictions. A candidate has his petition read in a stated (typically monthly) meeting, and an investigation committee is appointed and sent out with the expectation that they will report back at the next monthly meeting. Once they do, a ballot is held. If approved, the degree night is scheduled on the lodge calendar, and the candidate notified, initially by phone, and formally by a mailed invitation.
Once you receive your EA, then the schedule is in your hands. You must memorize and turn in the required proficiency lecture before you can advance to the next degree, and there is a 30-day/1 month waiting period between the degrees. I went through pretty fast -- 61 days from receiving my EA to my being raised as an MM, but I worked hard on the lectures, skipped few school nights, and turned in on time... and that's about as fast as it can be done here...