Automatically hold a product charge until certain number of delivery

A customer enters the product detail page to buy ‘Product A’ for $79.99. Product A is listed elsewhere on the site for $84.99 so they are entering this specific product page for the $5 discount. In order to buy this discounted product they must subscribe to a subscription plan for another product, ‘Product B’ They can choose a 2 month plan ($15.99) or a 3 month plan ($19.99) for Product B. The unique aspect is I only want to charge the customer the $79.99 for ‘Product A’ at checkout. I do not want to charge or ship Product B until the 2 or 3 month mark (depending on what the customer chose).