Timers would be a good solution for this, but they are severely limited with the 2-hour restriction. Allowing users to set Timers later in the future, (with a sensible limit of 24 hours, 2 days, 1 week?) would enable a ton of great experiences. It could be protected from abuse by making the api use a date/time utterance slot, so you're sure the user specifically requested the date/time for the timer.

The new Timers API allows skill developers to create a timer within the skill and on completion call a Task in a skill (via https://alexa.design/skillconnections)

https://alexa.design/timers
https://alexa.design/timersdemo

You should be able to do this soon via a scheduled routine as Amazon have announced their intention to allow users to add skills to a routine.
https://www.engadget.com/2019/05/06/amazon-alexa-routines-sunrises-email-alarm-smart-cameras/

Upvoted! I get many support emails from Alexa customers wishing to use their favorite ambient sound/sleep sound as an alarm.

Allow users to say "Alexa, wake up with {{Any enabled Skill name here}}."
Would this require developers to implement a specific intent?

and also allow skills to be opened from routines as well as alarms. eg when I say "alexa, good morning" after it tells me the weather it then tells me when my next train is