The default OpenWrt firewall does not block outbound connections, so NTP requests should work just fine (they do on all my desktops). If I'm not mistaken, you just added port forwardings, but did not alter the behavior of the firewall.
I would try to do a packet capture using tcpdump on the OpenWrt device and trigger an NTP request from the camera. I haven't done this for ages, so I'm sorry, I can't provide you with the necessary command.