For Call Parks on the 700 - 719 range, we recomend setting "Ring for" to the highest possible number, 7200 by default. 

For Call parks on the 720 - 729 range, "Ring for" decides how long the caller will stay parked before the caller is returned to the person who parked the call.

After the queue has been created, manage the queue user and make sure Voicemail is NOT enabled. If Voicemail is enabled, parked callers will hear an option to leave a Voicemail at intervals that match the "Ring for" value.