I find that I sleep better when I have about 90 minutes of sound to put me on the sleep train. I would love to be able to set my own shut off time for the sleep time instead of being limited to 60 minutes.
A similar idea has already been suggested here - feel free to add your vote to it! Keep in mind that it's Status doesn't mean it won't be implemented, as Spotify will check it out if it reaches the necessary amount of votes.
If you think your idea should be considered as separate, feel free to submit it again highlighting how your idea is distinct from the existing one.