Mine never took to my frogspawn in the 2 years prior to my first anemone. Of course these are Occs and I don't know if they were wild caught. Frankly, the few times they took any interest, the frogspawn would not fully extend out and did not look as cool.
It took my clowns 3 months before they went into the RBTA (plus another 3 months before the male took to it as well). When it is not the natural habitat of the clownfish, it is really hit and miss. But certain species are more likely to find a host quickly than others. What kind do you have?