All incoming calls would ring for 30 seconds (with a buffer of 8 seconds, give or take). However if the "Call Idle Agent" option is enabled, then the call would ring for 10 seconds for the first agent. If that agent does not answer the call it then moves on to the next agent and rings for another 10 seconds. This will happen until the 30 seconds of ring time is exhausted, after which a non availability message is played and the call is routed to the voicemail if configured.