Bill - We take our occupied maintenance seriously and as such require that all on-call techs be within 1 hour from the propety when on call. Regardless of the emergency.
We use an answering service that does a great job of "screening" the calls, weeding out non-emergencies and notifying the on-call when a real emergency does come up.
Our emergencies are as follows: Electrical (as in none or breaker trips, etc.), No Heat or A/C (regardless of temp or season), water issues (leaks, backups, or lack of), anything related to either the smoke detector or CO detector.
However, that said, our maintenance team takes pride in the fact that customer service is the name of their game. We carry a 24 hour completion policy on occupied maintenance orders and also keep a strong list of subcontractors at the ready.
Since your portfolio is sizeably smaller, it would make sense to keep a 24 hour policy on regular work orders and stick to the basic categories for emergencies, keepingin mind fair housing issues as well as liability concerns.