Run auto-schedule between specific dates

I sell a product which helps people to prepare for a once-yearly national exam. I know that there are a lot of people who try out my free software (and so complete the form on the website to join the mailing list) but who are slow to order it. I know that I get a very good response to giving them a countdown to the exam so I will run a series of emails "10 weeks until the exam", "9 weeks until the exam", "8 weeks until the exam" and so on. I want to set all these emails up and schedule them to be released at one-weekly intervals.

Now if someone only finds my site 8 weeks before the exam they will sign up to the email list and suddenly receive three emails with the subjects "10 weeks until the exam", "9 weeks until the exam" and "8 weeks until the exam". That does not put a very professional image across to my potential customer.

From a user interface perspective my suggestion would be to have a field on the Auto-Responder form for 'Auto-Responder Ends' followed by a date and time picker. The Cron job will then just need to check that the current date and time is between the chosen values before it executes the auto-responder.