Short answer: No.

The longer answer is that since Send Time AI is based on the (anonymized) behaviors of your individual contacts, you can have as many or as few as you'd like in a step or campaign. If the contact is one we've seen before, Motiva may already know what the optimal send time is, and if it's a new contact, Motiva will monitor their responses until the optimal time is determined.

Motiva only requires a minimum number of contacts when it is testing multiple emails or subject lines, and trying to statistically determine which of your messages is generating the strongest interest from your contacts.