@ross My use case is non-standard :-) For FediTest.org, I'd like to deliver outgoing ActivityPub messages asap, so my tests don't take longer than necessary. I've attempted to invoke wp-cron.php manually but it's not sending immediately ... 15 sec wait often works, but not always.
@j12t Sounds like you want an actual queue rather then job scheduling.
Trouble is the only queuing solution I know runs off of wp-cron!
https://github.com/deliciousbrains/wp-queue
Do you know what cron event your sending is hooked onto?