how long does it take for polygenetics to show significant results?

this is a super random question, and i don't intend for it to be about leopard geckos specifically (tbh if there's BP examples i'd appreciate that), but learning about their morphs was the first time that i heard the term.

how long has it taken polygenic morphs (like Tangerine? right?) to show real and consistant results? is there any history out there on this? is there info on other species where this happens with breeding?

this is probably an obscure question but thank you to anyone who replies!