It might sow confusion if we throw around term "traffic display" without being clear that we're talking about cellular network based traffic systems and not about proper ADSB-IN displays. Sure, any internet lags become clear on your EFB screen if you're running proper ADSB-IN at the same time. The position delay seems, in my experience, to vary from zero to several seconds.
But just to be clear, there is no latency issue with true ADSB-IN traffic displays (like SkyEcho2 or better).
And usually, when we're discussing the use of traffic displays in the circuit - for or agin - we're talking proper ADSB-IN
That being said, Area-51's story, a few posts up, shows that even laggy cell based traffic (like his AvTraffic/OzRwys integration)
can sometimes work better than any amount of "managing separation visually" : "After one more recent near miss, have upgraded the situational awareness by taking out a paid subscription with AvTraffic ... it paid dividends. The first flight afterward saw almost the exact same scenario with the very same other aircraft, however this time was able to see the situation unfolding well in advance, so simply turned away."
OzRwys is clear about the limitations of its cell-based display of traffic information. As they put it "OzRunways traffic is great
but it's not the whole picture" before going on to urge customers to invest in a proper ADSB-IN solution. But short of one of those, an AvTraffic/OzRwys (cell based) set-up does have a few plusses of its own, combining OzRwys targets with all other traffic supplied by the 'ADSB-exchange' (most ADSB-OUT equipped aircraft - depending on local coverage) and presenting it all on the familiar (already in use) OzRwys main map page - without need of other devices. Plus AvTraffic has aural traffic alerts. And while those alerts are probably very useful enroute, I can't see how they'd help much in the circuit; wouldn't Bitchin' Betty be having constant conniptions even in a mildly crowded circuit area?
I suppose time stamps could overcome lag issues in internet traffic displays (as long as pilots didn't have to do any maths in their heads, when only a glance may be spared) but wouldn't it just be putting lipstick on a pig? ADSB is here - it's an amazing aircraft-to-aircraft tech which just works, is user friendly and is heaps cheaper than it used to be. The problem remains that it's far from universal in VFR land. Too bad the proposal before government years ago for supplying devices free for all VFR aircraft wasn't taken up.