It can take months to years,wait until all the twitching has finished this will be when the small one has conceded that the large one is the more dominant and the female.there are a couple of things you can do to help the mating process.
you need to mimic spring time in the tank.
try not to clean the tank too much apart from the front glass
drop salinity to 1.020
feed the clownfish more than usual,but keep water quality good.
raise temp to 80
All this will make the fish think there is enough food for their fry to survive and will help.
you will then notice the clowns cleaning one spot in the tank,usually some LR
If you want to breed put a terracotta pot in there to try to encorage them to spawn in the pot,this will help you in the future.then research alot.
A few things you will need for breeding/raising fry
a couple of small tanks
rotifer cultures in salt buckets
brine shrimp cultures
2 terracotta pots