The CBSE is offered twice a year (spring and fall)...you can take the test multiple times and I believe you send only the score you want the programs to see. Most of the externs we get take it about 3-4 times before applying...though I don't think more than that would be foolish (just brutal). Taking it too early would be a waste of time/money. I know some people take it not having studied at all just to "see where they're at"...I don't like this...seems like such a waste of money and a Saturday.
The MATCH is the January/February of your 4th year (~4-5 months before you graduate) but the application cycle opens your last summer of dental school (~12 months before you graduate) on June 1st. Ideally, you should have everything submitted as soon as you can. I think I had everything submitted for anesthesia by mid-June except my "letters of rec" which came in at the latest by the end of July.
D1 Fall
-do well in your basic science courses
-join clubs/research...but not at the expense of your grades
D1 Spring
-do well in your basic science courses
-clubs/research
D2 Summer
-Start spending time with your local OMFS department...you could certainly do this D1 year, but you'll probably be busy studying
D2 Fall
-Begin preparation for CBSE
-Continue to spend time with your home program
D2 Spring
-Take First CBSE (I wouldn't take your first CBSE until you've made it through First Aid twice, Uworld twice, and Pathoma/Goljan Once)
D3 Summer
-Really study for the CBSE
-You can Extern at this point, but as I've said before I think it's better to have a very respectable CBSE score going into an externship because a lot of attendings will ask you what you got while you're externing...and if your answer is sub-65 it could be the one thing they remember you for
D3Fall
-Take Second CBSE...hopefully get 65+
-Externships (do not make your first few externships at what you think will be your #1 choice...it's not really fair but residents/attendings will largely judge you on your experience/knowledge/usefulness...even when you really haven't had exposure to the field...in Shreveport we definitely think a lot more of the externs who can actually lend us a hand in the ER/Clinic/Pre-Rounding)
D3 Spring
-Take Third CBSE...hopefully you crush it...you can retake it the Fall of your D4 year, but I think a lot of times the results come after programs have already picked out their interview invites
-Externships...once you know what you're doing, extern at the places you really want
D4 Summer
-Apply early as you can. Programs have "deadlines" but usually they've already selected people to interview and will only consider a late application if it's shockingly good
D4 Fall
-Interviews
-Retake CBSE if you must
D4 Spring
-Match to a program crappier than Shreveport...pretend to be happy with your life...die a little on the inside
I'm not the ideal person to ask on this stuff...so if I made a mistake someone feel free to jump in and correct me...there are parts of this timeline that I could be very wrong about