Since you said you want to alert them each day, then a daily job that runs your "daily alerts" might be the way to go. It would simply query on the ones where the order is pending and was started started in the last week, loop over those and send out alerts based on the original start date compared to the current date, and apply the appropriate points at the same time. cronjob that calls a PHP script isn't a bad idea here. Your query could return the number of days elapsed to make the alerting process simpler. To me, this does fall into a day-to-day schedule... just the results are different each day.
Note of caution: if you do alerts, you have to give them a way to opt out of those (unsubscribe), so your alerting process would need to take into account anyone who has opted out and NOT send those any further alerts.