Hello. The delay setup in the ILG really has nothing to do with how the phones ring. Check the DIT settings in the Trunk Assignments to see how where the lings ring to.

You are correct, depending on how the extension is setup the phone will either pickup a CO line or the Intercom key. If you are entering a feature code then you should just press the Intercom key before entering any feature codes. The phone should return with a few short stuttered dial tones if everything is OK or a busy tone if something isn't right.