Official comment
Our Certified Consultant Neil Kristianson answered this question in another forum:
Yes. You can schedule a charge for a later date...
If you're using the manual transaction just hover over the Total Charge amount. A Charge at a Later Date box will appear. Here you can pick any date you want for the charge. The same thing can be done on a standard Smart Form so anyone who fills out that form will be charged on one specific date.
The other option is to offer a free trial period. Here you can pick the number of days in the future you want them to be charged. This way everyone who fills out the form will have their own unique charge date depending on what day they purchase.