Literal translations:
* L'amour prend du temps: This is the most direct translation, meaning literally "love takes time".
* Il faut du temps pour aimer: This means "it takes time to love".
* L'amour se construit avec le temps: This means "love is built over time".
More poetic/idiomatic:
* L'amour est un jardin qui prend du temps pour fleurir: This means "Love is a garden that takes time to bloom".
* L'amour ne se précipite pas: This means "love doesn't rush".
The best option depends on the context and the tone you want to convey.