You can already do this, in the Trigger Booking Fields criteria - set it for when Number of Nights > 1.
Add the option in the Triggers feature to send a 2nd day message checking in on guests and how their stay is going, only if the reservation is longer than 1 night.
Currently there is no setting to send this message ONLY if the stay is more than 1 night. (If sent for 1 night stays the guest would already be checking out).
You can already do this, in the Trigger Booking Fields criteria - set it for when Number of Nights > 1.