Most likely UDP ports are blocked. Some of these devices will only stream over UDP, others can failover to TCP, which is what you are seeing when start time is very long. You have to open all UDP ports (0-65535) on the server, and you might have to map them to you Wowza server in your network, e.g., port-forwarding in a router.
Test by playing in VLC. There will probably be a long start time there too because it will fail-over to TCP. When it starts, look at Tools > Codec Info. You will probably see two audio and two video entries, that is a good test to see if it is failing over, which you don't want. When you get UDP ports open and mapped as necessary, it will start quickly and you will see one set of audio/video in Codec Info.