A section 35 WILL get you the help you need but you will be held for a period of time until a bed is made available either at Bridgwater (MASAC) or the Mens Addiction Treatment Center in Brockton. I believe there are other locations as well but these are the ones I am most familiar with.
I think the answer to your question depends on your previous criminal record of whether or not you have received jail time for the previous larceny offenses. If a nominal amount of bail is placed on your open matters while you are receiving treatment during your section 35 then you may receive credit for the time you are "detoxing".
In my experience, a person voluntarily sectioning himself/herself is usually a helpful fact if there is a plea bargain and disposition in the future on an open case. Completing the section and the accompanying aftercare recommendations shows the court that you are serious about your sobriety, and if you are already in some sort of aftercare program, many judges would be hesitant to pull you out of that program in order to send you to jail. If you do section yourself, make sure to let your attorney know about your plan so that he/she may plan appropriately, especially if you need to section yourself before your next court date. If you need help, get help and do not put your health at risk by waiting until the next court date to get help.
You are helping yourself which is good no matter what happens. whether you recieve committed time will be up to the ADA and the judge. Most of it will depend upon your criminal history and the current charges. good luck and take care of yourself, you have one life try and make the best of it.