I run into the same problem today, setting up my presence detection. In the end I found out that it works perfectly with a slightly different iptables rule:
sudo iptables -I PREROUTING -t nat -p udp --src 0.0.0.0 --dport 67 -j DNAT --to 0.0.0.0:6767
Source:
Now I got presence instantly when my smartphone connects to the wifi.