Note that if you're using caller ID on loop starts you'll always lose about a ring and a half before the desk phone rings. This is because the system is capable of routing based on caller ID (calls go to vmail whenever your ex calls, for example). Since the caller ID info comes from CO between first and second rings the system must wait for that info before routing calls, even if you're not using that routing option. Prove this by temporarily turning off CLID in the system (SYSTEM/DEVICES/TRUNKS/<TRUNK NUMBER>/SERVICE TYPE), you should start to see immediate ring.
One other thing that can impact is if you're using a STAR app for scheduling...my experience is that sometimes the processing time can be noticeable.