There are two main types of suppositories, and the answers depend on which kind you insert. Most commonly, anal erotics use glycerin, because they are wanting the feel of insertion, and feeling them in the rectum. These usually cause you to have a BM in 15 to 30 minutes. You can insert more, for faster results or to induce rectal cramping. Glycerin supps are classified as rectal evacuants; i.e. they cause the muscles of your rectum to contract and spasm, inducing a BM. They are great for a quick BM, but will NOT clean you out. Even if you stuffed the whoole jar of 50 or 100, it would not cleanse your colon. (I definitely do NOT recommend trying this: you'll wind up in the ER!
The second major type is the bisacodyl suppository, Dulcolax being the most common brand. These actually contain the true laxative, bisacodyl. These, too, usually cause a BM in 15 to 30 minutes, but if you force yourself to hold them longer, they work beetter, because your rectal lining is absorbing the laxative. It circulates in the bloodstream, and causes the entire colon to work overtime. Whereas glycerin supps usually produce one BM, these will produce two or more. Inserting more suppositories incrreases the amount of laxative in your system, just as taking more of an oral laxative works better. The main advantage to rectal vs oral introduction is speed of results. I have played with these, and find holding 2 for one hour cleans me out completely, but you will get cramps. One does a fair job, four gave me the anal "dry heaves" for several hours. I use these to punush a wayward sub.
The main disadvantage to Dulcolax is cost: about $1.00 per suppository. However, if you look online, there are generics which are just as good, as cheap as $15.00 for a box of 100. If you decide to try more than two, wear a Depends! You might just explode into your pants without warning!
I find that inserting one bisacodyl supp about 30 minutes before an enema series make the enemas release quicker and more completely, allowing more enemas in less time. I think the enemas clean me out better, too.