When a parked caller is left in the parking orbit for a specified amount of time, it is possible for the system to return the caller (Ringback) to the person who parked the call.
Calls parked to Queues in the 720-729 range have Ringback enabled. To activate the setting edit the ring timeout for the owner of each park (the user with the extension number of the park) . This is how long the caller will stay parked before the caller is returned to the person who parked the call.
In Call Park Queues that use the range 700-719, the 'Ring for' setting will control the time interval between system prompts that allow the caller to leave a voicemail.