Kural - 481

A crow will conquer owl in broad daylight;
The king that foes would crush, needs fitting time to fight

Explanation
A crow will overcome an owl in the day time; so the king who would conquer his enemy must have (a suitable) time.

Tamil Transliteration
Pakalvellum Kookaiyaik Kaakkai Ikalvellum
Vendharkku Ventum Pozhudhu.