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The dwell time is the time the ball is in contact with the rubber.
Which is why it's then weird that we are taking an estimate of the actual dwell time from a video of a head on collision of a ball with a blade with no rubber on it. Literally the one way of doing it that is likely to produce the shortest possible "dwell time".
I know the original topic is for the dwell time of different blades, but I think at some stage we have to accept that the original question isn't really meaningful, because in a game of TT, the ball isn't supposed to be contacting the blade directly anyway.
And while the blade MIGHT affect the dwell time, just hitting the blade head on with a ball is probably not even a remotely enlightening model of how long the ball is in contact with a rubber.
Which brings us to:
There ist scientific evidence that the dwell time is quite constant at about a thousand of a second.
This is so short that I highly doubt that anybody is able to recognize differences in the dwell time by playing with different rackets.
For me the concept of dwell time therefore does not make a lot of sense.
However what you really notice is that at the point of ball - racket contact different amount of "deformation" is taking place: at the same amount of force softer rubbers stretch more, flexible blades bend more,...
So my guess is that players feel that there is difference in the amount of "deformation" and the term "dwell time" is used to describe that, although there is scientific evidence that more deformation does not necessarily take more time.
Do you have the actual study, or the context for when he made this claim? While I believe in the scientific rigour of whatever study he may have performed, the actual methodology matters a lot, and tells us a lot about what exact conclusions we can reasonably make from the results. If he did something like bounce a ball from some bats head on, then it might well be correct to say the dwell time remains mostly constant between blades, but in reality it would be a poor model for actual contact in a game situation, and actually tell us very little that is useful. If instead he took lots of extreme high frame rate video of a wide range of people playing, then it would be very compelling evidence.
And as BB eluded to, the actual variance of these contact times, it makes a lot of difference exactly how much this time is expected to vary (assuming good and useful methodology). The mean contact time might well be 1ms, but like if BB said if this is 1ms +-1 ms, that is a pretty big difference between a long and a short contact.
Also lets all be clear, your hand is not actually touching the ball, so irrespective of how long the actual physicial contact time is, be it 1ns or a whole minute, we will never 'feel' the actual contact, it's always inferred, the actual physical dwell time is irrelevant to whether or not we can 'feel' the contact, you are always just inferring it from whatever you do feel, be it vibrations in the blade or just the slight decceleration of the bat.