Even if this was long ago I’ll post an answer.
After some digging in the wordpress cron files I found the following:
* wp_schedule_single_event is using microseconds instead of seconds as the documentation says.
* Arguments must be passed as arrays. My php/apache error log was warning about some executed array functions on non-arrays. It’s do_action_ref_array that is used by the scheduler code that requires arrays as arguments. This is also not documented.