Actually, with Stripe and Amazon they will just hold on to the information and not authorize/charge so you can wait much longer (like Kickstarter). The downside

Actually, with Stripe and Amazon they will just hold on to the information and not authorize/charge so you can wait much longer (like Kickstarter). The downside is that you aren't guaranteed to be able to charge the amount at the end, but I don't think that's likely to account for the majority of your customers.