There are some good books out there on the subject of breeding clowns. I will try to look them up for you.
This is true that they will become a pair when they are sexually mature. The time frame for this to happen is not the same for all fish depending on the diet, health of the tank and the size of the tank. At a years time they should be able to breed, again depending on conditions.
To get them to breed they should not be in a comunity tank of course for obvious reasons. Water peramters should be stable with plenty of places for them to lay.
My first breeding of clowns and Damsels was back in around 1980. It was actually a fluke that it happened. But fun.
Here is a link for some further reading on this. The one thing that I dont agree with is the enemone.
http://www.netpets.org/fish/reference/saltref/brdclown.html