I’m reading the specs on Steinberg audio interfaces and they keep saying zero latency.
Unless steinberg have discovered something there is no such thing as zero latency.
Physics tells us this is not possible. The ASIO software takes care of the latency sync the I/O
So, Does anyone know the physical latency of the Steinberg interfaces ?
Of course there’s latency! 
But in respect of timing while you’re playing your instrument it is more than adequate and essentially zero. It has DSP chips, so if you know you’re DSP theory (which sounds like you do). Granted it is more prevalent for drums and perc. What they mean is that you hear what you’re playing instantly and not going through the computer system (DAW), which I’m sure you know. I would say, an educated guess, the latency would be in the micro seconds. So not a problem for me anyway. Whereas my previous Tascam interface boasted zero latency but was at least enough for timing issues 
. I would say that was in the tens of milliseconds.
Anyway, feel free to disregard my comments. 
Well, I think the “zero latency” you are referring to is “zero latency monitoring with DSP effects”. Which means the effects are applied to the inputs directly in the unit and sent directly to the speakers (without going through the computer). This, of course, is not ACTUALLY zero latency but, as mentioned above by Fuzzbox, it is VERY low and negligible to human ears (like a digital guitar effect stomp-box or rack unit effect).
If you want to know the latency of the unit through the DAW (i.e. ASIO) then it depends on the settings. With 44.1 KHz, the buffer can be set as low as 32 samples which yields a system reported round trip latency of about 5.5-6 mSec. At 192kHz, the buffer can be set as low as 128 samples, which yields about the same total round trip latency.
Of course, most modern units are capable of very low latency that is almost not even a factor. But, the bigger issue most often is whether the machine the DAW is installed on is capable of processing the audio fast enough to prevent audio dropouts.
Hhhhmmm… 418 Carrier Landings. 
Pilot, Fleet Air Arm?