When is the best time to evolve staryu?

Answer 1

you must make it happy and to do that follow these rules:

Don't let it FAINT

give it the soothe bell to make it happy quick

let it battle by its self

train it in the morning or noon that's the time it will evolve.

and by you do all of these things it is possible it will evolve by level 30(not exact)

Answer 2

probably before a gym that he's good against

but maybe before that lvl him up with exp share

Answer 3

In the GBA games I'd say Level 46. In the DS games, I'd say Level 55.