Another user asked for this feature recently and I gave it some thought. Unfortunately it would be quite involved to change Dailymail in that manner, and would likely introduce new bugs into what has come to be a very stable process. Dailymail was designed to run just once per day, and the rest of ListMail was built with that in mind. I do see the value in the feature, though, so it may indeed be implemented in time.
I came up with a possible hack that could work without modifying ListMail.
1. The Dailymail cron task could be set to run with the (undocumented) &nosched=1 option to suppress scheduled message processing.
2. A separate script set to run more frequently for scheduled messages alone could be created.
3. The time to send a scheduled message could be added to the Subject line of the message, and be removed at sending time. This would eliminate the need to modify the UI or database with new fields for time.
Basically the script in #2 would check for scheduled messages as per usual with the addition of checking the subject line to see if the time to send has been reached or passed.
Unfortunately I didn't complete this hack for the user, so I can't provide any code.
I am currently working on a new support system and other things on the main site. Perhaps after that I will be ready to take on some custom work such as this.
