Discerning a difference between streamers is difficult...only me or common for all?

What timing smear? Is it correcting something that happened in the recording studio? Phase issues with the mic. and other processing done during the recording? That’s where the low hanging fruit would be. Orders of magnitude more time smear than anything happening electronically during playback - at least until your speaker and its crossover network get ahold of the signal. At that point, unless you’re fully active with FIR filters phase correcting the drivers, it’s time smear O-Rama! Better have your ears at just the right height for all the drivers to time align, or have a head tracker that adjusts the timing of the drivers as you move. Even with all that working as best it can, you'll still have vastly more time smear occurring in the speaker trying to get the sound to your ears than with the digital cables will cause. And the room, if it's not anechoic, is going to blow all of that out of the water. But we'll assume that it's only first arrival to the ear that counts for now.

With all that said, I'm not claiming the cables can't sound good. I just need further clarification on why time smear would normally be an issue, and what evidence is there for that as a typical cable issue.

As Tim what brand digital cables are you using for Ethernet ,usb, ?

There you go, another perfectly interesting thread infested by cable zealots

I'm using HDMI out of my computer into a receiver. I'm not sure what brand it is. Some very basic HDMI cable that costs about 12 bucks and can handle 8 channels of audio at 24/96 along with a 4k HDR video signal. So I'm definitely not saying my system is one that might reveal issues with cables and streamers, although it definitely does concerning the HDMI cable from the Blu-Ray player to the TV, whe I can see and hear static sometimes when the cable needs to be jiggled to make it go away.

On better systems, where cable time smear might cause easily audible issues, what time scale are we talking about? Millionths of a second? Is this smear that would cause data errors? From what I've seen in testing it's not hard for a cable to get up to a million hertz while still maintaining excellent phase and amplitude fidelity. 

Only if you use coax from streamer to DAC where jitter begins to matter. Otherwise all PCs are identical. CPU does not care if power is linear or switching. Internet does not tell of this is audio, video, jpeg or a Word file, all sent the same way. USB optical isolation may come handy in some cases.