I bought a pair of convicts at the lfs. Chose 2 fish - male that was one of the largest in the tank AND was staking out territory already and on the other side of the tank there was a comparable-sized female that was also guarding a dug out section of substrate.
Bought them and put them in a 75g tank with a 9" oscar, a 3" firemouth and some other small fish. The oscar and the firemouth made it into Convict vs. the World - so they paired off quickly and adpopted a small stump to hang out in. They were in there for about a month, then I moved them into a 29g tank and within 4 more weeks there were fry in the tank. I did not use a clay pot - they found a hole in a nice big, algae-ridden resin stump you buy at PetSmart - and they seemed to have no problem.
I also keep 6 red-tail tetras in the tank along with an ottocynclus(sp?) catfish. The tetras seem to be able to stay out of the way of the marauding convicts as they patrol the tank like coked-up security guards ensuring that nothing is moving in the tank but them and their fry. I think having the tetras enables the convicts to take out the hormone agression on other fish besides each other (or the fry for that matter).
Any how - the short answer was - about 3 weeks if they are the biggest thing in the tank.