Automated email and Cron Jobs

I have a membership site where members have to manual sign up every year. I use wishlist member to hadle the memberships. The only issue is I need to be able to send out reminder emails about membership expiring about 1 month prior, then about a week prior, then after it expired. I assume I would have to use some cron job to automatically check the user’s registration date and determine if it fell into one of these 3 groups, if so, send an email reminder. I haven’t been able to find a plugin to to this. Any help would be greatly appreciated.