You get a handwritten one on the day. The wedding officer (pastor etc) takes all the documents to Home Affairs and to register your marriage. Never heard of a couple doing this themselves and not even sure it'll be allowed/legal. Why would you?
If your marriage officer provides the service you can, for an extra fee, get an official marriage certificate in about 4 weeks and an unabridged one after about 6 weeks.
1) The Marriage Officer issues the couple with a hand written marriage certificate on the form DHA-27 (abridged - half-page) on the day of the wedding.
2) The Marriage Officer takes the Marriage Register Book DHA-30 with him to Home Affairs within two business days of the marriage and gets all 3 copies of the marriage register stamped by the Home Affairs Marriage Official. Home Affairs keeps the top copy, the Marriage Officer must give the middle copy back to the couple, and the bottom copy stays in the book (until that is also eventually handed back to Home Affairs). Home Affairs can take up to two weeks to register the marriage on the Home Affairs Marriage Database.
3) The couple keeps the hand written copy of their marriage certificate(DHA-27) AND the copy of the Marriage Register (DHA-30) in a safe place.
4) When the couple wants to apply for a printed marriage certificate, they complete form BI-130, and take it along with the copy of the Marriage Register (DHA-30) to Home Affairs and pay the R75 fee for their printed marriage certificate. This process can take several months.
Many couples do not apply for the printed certificate as the hand written one serves them just fine.
Couples are not supposed to handle or be in possession of the Marriage Register documents until after they are submitted by the Marriage Officer and stamped by Home Affairs. I know there are Home Affairs branches that may bend this rule, or exceptional circumstances that may require the bending of this rule, but usually the Marriage Officer should not let the Register Book out of his possession since it was issued to them in name directly.