Here's the concept of the "Too busy right now" feature:
- Create a list, name it something like "Reminder subscribers"
- Create 2 custom fields, Reminder Date (Date) and Days to remind (Text)
- Create a 'Send on date' autoresponder .
On the frontend where you collect the user's email, you need to detect the user's timezone on the frontend using javascript (this will help → http://pellepim.bitbucket.org/jstz/).
The user will subscribe to your list with their email while passing in their email and timezone data into your backend script.