My dad was a pilot on Lancasters. He talked extensively about his experience. I saw his pilots watch and it did not have a stop watch. Furthermore, over the target, communication was disciplined and professional. Up until he died a couple of years ago, I was in regular with dad's navigator. I'm pretty certainly, the time they were within 90 seconds of the the target, communications between the 3 crucial crew members at that "time" (pilot, navigator and bomb aimer) was about time and distance to the target, minor course adjustments, defences, and so forth. The last thing the pilot is doing is playing around with a stopwatch. Amd if you thing about it, in the dark how visible is the ticking hand of a stopwatch however much luminosity it had?