It’s never too early to reach out, but timing can make a difference. A good time to contact labs is 4-6 weeks before a new semester. If you are looking for a summer position, you may want to reach out as early as December to make sure you have the opportunity to apply for any relevant summer programs or fellowship funds, which often have January and February deadlines. That said, many labs accept students on a rolling basis, so if you're interested, don’t hesitate to reach out—just be mindful of busy academic periods like the start of the semester or finals. Even if a lab isn't taking students immediately, reaching out early can put you on their radar for future openings.