That evening, JT made 2 identical trips to her apartment. On her second trip she would have been stressed knowing her youngest was ill and half an hour later she would learn another child had been abducted.
She would also have experienced group pressure to pinpoint a timeline, possibly resulting in too much emphasis on her 21.15 trip and a possible false/muddled recall. (I imagine for the McCann family an earlier Tannerman would have made them feel better about their lack of later checks & for JT the fact that neither GM or JW noticed the man, would have made her feel less bad for offering information of seeing someone walking away with a child).
IMO there is a very real chance that the actual sighting of Tannerman was at 21.50 and that the lighting JT saw was from a street lamp. I think this because any premeditated abductor would likely have favoured the darker/less checking “window” whilst the main meals was served/eaten. (Obviously, not counting on JT gobbling down her meal to swap with her partner).
It would also explain why JT and the Smith family subconsciously took more note of the man and scantily clad child - than they would have done, say one hour earlier in the day. Also, the Smithman/Tannerman description is almost identical making it likely that they may be the same person. Additionally, if Tannerman looped back around the street above - it would have put him on course to bump into the Smith family at pretty much the exact time that Smithman was witnessed.
To me at the very least, this alternative sighting timing should have been considered as a possible hypothesis. As a later Tannerman sighting would have indicated the possibility of an accomplice (due to child’s body position), no use of a get away car and a perp that likely lived in the vicinity of the Smith sighting so likely a local, plus they would have had two/three efits of the abductor. (This one small detail, if it was muddled, could be responsible for why this case has taken so long to solve/unravel).