This appears to have no syntax for X minutes past the hour, and the like. Even more than cron, this would encourage writing a thundering horde of jobs that all trigger at midnight?

Cron's syntax lets you easily calculate the next time a job will have to be run (rather than eg re-checking schedules each second, as in the earliest crons). However, exact timing isn't always necessary or desirable - eg in this case, encouraging all users to run jobs at exactly the same time.

I wonder if there is room in the plethora of cron alternatives for one whose syntax encouraged users to schedule jobs eg 'overnight' and left it up to a scheduler to spread jobs evenly? So eg, 'every hour' actually meant 45-75 minutes between executions.

Something similar happened with g_timeout_add_seconds and tickless idle; there the idea was to gather scheduled events to clock second boundaries, to avoid cpu wakeups-because really, users didn't care that they needed the timer to run exactly n seconds from now.