I read the pricing FAQ but I'm still a bit confused.

Here's my use case:

I host my own web apps & sites.

I would like to use WebFlow to redesign one of them. Should take me about a month.

Do I only pay for a month, and then export, and then quit paying?

What happens when, 1 year from now, I want to tweak the site? Can WebFlow import old webflow projects? Or do I need to pay for every intervening month to preserve the ability to use WebFlow on that site in the future?