Although heavily requested, Behringer obviously does not provide a firmware update to the XAir series which includes an output delay.
There seems to be a workaround (not verified) for a simple delay line: using the stereo delay e.g. on bus 5/6 (XR18) or 3/4 (XR16) or LR and using LR as source for Aux 3/4 or 5/6 in output routing:
As the settings needed (changing output routing, correctly enabling the delay FX inserts, delay settings) are not easy to remember for occasional use, and the delay time is rather difficult to dial in (0-3000 ms knob, for a delay line 0-300 ms should be more than enough) while other knobs are not needed (like all the Feed values):
Would it be possible to add the output delay as an FX, or even better in the "Main" tab of the Bus and LR settings, with reduced parameters (enable, time, lo cut, hi cut, mono/stereo/crossover, gain/volume) and routing/FX slot 4 settings automatically adapted when the delay is enabled?
(BTW, selecting the stereo delay FX for two Busses gives 3 (not: 2) options for insert enabling, which is not understandable.)