If it's as low as 150-250ms that's pretty good. My DTR radios have latencies over 1 sec.
If using a DMR radio on a duplex frequency pair(Receive and Transmit frequencies) the radio will send a series of packets(My CS-700 transmits 4 times in about 2 seconds and then give a 'bonk' until you release the PTT if there is not a repeater in range) to sync time slots. If there is a DMR repeater with in range, it will reply, in between sync packets from the subscriber, to sync up.
Once sync'd, the radio will transmit and start sending voice data.
I would guess on a repeater, from PTT to hearing voice, needing only 1 sync transmission, would be around 400ms. Anything longer would be caused by the repeater not hearing the subscriber transmit its first sync packet.
If using a DMR radio on a simplex frequency(Receive and Transmit frequencies are the same) the radio will just blindly transmit(At least my CS-700 does).