Add start date settings for UC Node Access features

Issue Summary

Hi,

I'm creating a subscription site like an online training site. Here's how it will work: every new subscriber (no matter when they subscribe) will first receive lesson #1, then lesson #2 two weeks later and so on. Then at the end of the course the subscription expires.

I have a solution which I described here: http://www.ubercart.org/forum/ideas_and_suggestions/4815/online_training.... However, I could end up with 60-100 roles (including renewals and various types of subscriptions), and I'm nervous about managing this many.

I'm hoping there's a much neater solution by extending UC Node Access, so that subscribers gain access to an additional node every two weeks (or preferably at a configurable timed interval).

I've tried creating a custom Workflow-ng rule, thinking that the 'event' could be the subscriber being granted the "subscriber" role by Ubercart, the 'condition' could be the number of days since that event, and the action could be access to a new node. And other variations of that idea.

However, this is beyond me.

Can you help? I know I'm asking a lot, but it would be a neat additional feature for other UC users and I'd be very grateful.

Thanks.