The link could also give you the ability to bring your userbase back to your site.

Clearly on the mobile or something, not as important. But bringing them back via the web page. Allows you more options in terms of what to display.

I know you haven't mentioned nor asked. But a potential tier pricing scheme.

1) How many reminders per week / month

2) Maybe allow non paying users the ability to pick 15min blocks, yet allow paying users the freedom to create any.