>Is there anybody out there that can give me a simple explanation of 
what the setting "retries allowed after runday" mean, when selecting 
calendar scheduling.

Yes, in this context, a "runday" is a day on which a calendar based 
schedule should run. 

 - you have a calendar based schedule that denotes that a backup
   should run "today"
 - you have the backup window open for "today" at 23:00
 - the backup starts at 23:10 and fails at 00:10
 - the "retry after runday" option determines if the failed backup 
   is allowed to retry because the day is switched. The default 
   retry configuration is "two retries in 12 hours". 
 - note that for the retry to happen at 00:10, the window must be
   open at 00:10 to allow the retry. 
   
With pre 45_MP2 installations, ALL calendar based schedules needed 
the "retry after runday" option ticked, otherwise the backups 
wouldn't even run ON their runday. This is fixed in MP2. 

Regards, Joost
-- 
Long may you run.