Unfortunately, AD connect doesn’t have a ability to change it schedule. For SCSM 2010 AD connector runs one per hour, for SCSM 2012 it run once per 24 hours. For small domain this is acceptable schedule but for large domains with many users it can be potential risk of overload of the SQL or SCSM servers. AD connector get from AD only objects changes since last run but even this amount of data can be large and reduce workload to SCSM management server and even more to SQL server.
Sometimes you need to know which objects contain the queue. This can be done easy with PowerShell.