DMX binding slow to respond

I have a rule that detects PIR contact and then sets a DMX dimmer to a certain value :-
if (HourNow < 6){// Midnight to 5:59AM - DIM
sendCommand(DMX_07_Dim, 2)
sendCommand(LozDimmer, 20)
The channel DMX_07_Dim can take up to 10 secs to actually be sent from openhab. the second line is a mysensors thing and acts at once.
If I run QLight commander I can get instant response from my DMX dimmers using the ARTNET protocol.

Anybody have the same issue? or a solution?