Hi… As far as I know, the [[schedule]] syntax attempted in the first quote does not exist, 
, nor is there a conceptually analogous substitute available within the bounds of fly.toml, really.
Over in fly m update, there is a flag of that name, but it’s limited to coarse-grained --schedule=monthly and similar. You cannot specify cron selectors with a particular day of the month—or fancy choreography of that kind, 
.
https://fly.io/docs/machines/flyctl/fly-machine-run/#start-a-machine-on-a-schedule
Perhaps you were thinking of the much heavier-weight Cron Manager, which debuted a year ago?