My advice: your trial should be a minimalist version of your product with an unlimited duration. When a user signs up for the trial, add them to your mailing li

My advice: your trial should be a minimalist version of your product with an unlimited duration. When a user signs up for the trial, add them to your mailing list. Then, when you add features 1 month, 3 months, 6 months from now, you can mail your users about them, and that user can log back into his trial account to try it out.