or EctoJob - if you want/need persistence (which afaik quantum doesn’t provide) EctoJob: A transactional job queue built with Ecto, PostgreSQL and GenStage (or Rihanna https://github.com/samphilipd/rihanna that afaik works somewhat similarly)
there is also SchedEx https://github.com/SchedEx/SchedEx
I use quantum for fixed scheduled jobs (eg every hour) - and would probably go for EctoJob for on-demand scheduled jobs… ymmv obviously