When is the best time to apply for an internship?

You can do it when you are into final year of your course. By this time, you will have most of the knowledge and maturity to understand the corporate work culture.

It’s never too early or too late to apply for an internship. I think this decision should be more based on you, and whether you are confident in your major. If you’re not sure what you want to do freshman year, then waiting to apply is the right way to go. If, however, you already know exactly what you want to do, then you can apply the summer of your freshman year. Best of luck to you!

It's never too early and it's never too late. Most students start their internships between sophomore year to junior year. But experience is experience and the more of it you get the more you will learn and increase your chances in landing a job of your liking. Don't be afraid to apply for an internship for the summer after your freshman year, for that I would suggest applying around January time-frame and keep applying. You also have the option to volunteer during that time or help conduct research for a professor in a field of your liking.