Ask HN: When is the best time to start looking for summer internships?

Hey, I'm wondering when do you think it is the best time to start looking for an internship, on the second year of university, the third?

Has anyone done an internship on the first year summer?

Lastly, when do you think it'd be advisable to start looking for companies and sending CVs, late fall, early start of the year...?

Thanks