I've tried to come up with a way to change it for each page you submit, but I haven't come up with anything that doesn't require pop-ups or page refreshes. I really would like to keep the UI as simple as possible. Is it too much work for the user to add the delay to the end of the url, ie example.com#DaysToSend=1, hit refresh, then hit the bookmarklet?

is there a service that sends me daily summary email with links?

That sounds alot like Read it Later: http://readitlaterlist.com/.