First, this opening is not legal, and unless the AHJ has explicitly approved it and the exemption is on record it needs to be changed.
1. Delayed Egress is strictly defined in NFPA 101 as needing signage at the door, ie:
2. If not on the door, the button itself also needs to be clearly identified (even lighted) as the trigger for door release, ie:
3. There also needs to be an alarm sound for the delay period.
4. Also, the door needs to have emergency lighting.
If any of these four points are not present, it is illegal.
A 30 second delay is not typical, and while approved under code, typical requires explicit approval of the AHJ (Fire Marshal) and is almost always 15 seconds.
Here's the IBC excerpt specifically laying out delayed egress:
IBC – 1008.1.9.7
Approved, listed, delayed egress locks shall be permitted to be installed on doors serving any occupancy except Groups Assembly, Education and High-Hazard occupancies in buildings that are equipped with an automatic sprinkler system or an approved automatic smoke or heat detection system.
- A building occupant shall not be required to pass through more than one door equipped with a delayed egress lock before entering an exit.
- Doors unlock upon actuation of the automatic sprinkler system or automatic fire detection system
- Doors unlock upon loss of power controlling the lock or lock mechanism
- Door locks shall have the capability of being unlocked by a signal from the fire command center
- A delayed egress lock will prevent egress for 15 seconds (or 30 seconds when approved by the AHJ) when initiated by a 15-pound force
- Initiation shall activate an audible signal in the vicinity of the door
- Once the door has been released relocking shall be by manual means only
- A sign shall be provided on the door located above and within 12” of the release device reading: PUSH UNTIL ALARM SOUNDS. DOOR CAN BE OPENED IN 15  SECONDS.
- Emergency lighting shall be provided at the door
Let the customer know they have a door that doesn't meet code. Ask them why they need delayed egress on this door to begin with. On your own, confirm the AHJ approves delayed egress in the area. (Again, start with the fire marshal.)
You are procedurally correct on the power interruption design of the pushbutton. The button should directly interrupt lock power, not control an input contact on the controller.