This may sound like a dumb answer but it depends what you are looking for and how you are looking.

If you are specifically talking about Garters than no it is not a good time. Of the hundreds if not thousands of snakes I have found at night (usually roadcruising), only a hand full have been Garters. I have found the best times for Garters are in the morning when the sun is popping out or at dusk when they seem to be on the move from their basking and hunting grounds to the cover for the night.

There was a nice meadow I visited at dusk recently that I found a Garter under nearly every dried cow patty I flipped. Not the most glamorous of herping tecniques but it works well.

-Thomas