Here you are talking about the transmission time of potential sensory stimuli to reach an observer. Before the observation products can be generated by the observer.
When an experiment is conducted, just one parameter should be changed. The one thing being investigated. If that is not so the test is not fair and the results untrustworthy. You would not think it fair if a comparison of duration of an event was conducted using two identical mechanical watches, one immersed in very fine mineral oil- the other in thicker oil. The clocks on planes experiments show a material change has happened not just a signal delay effect that would have the clocks tell the same time when reunited. A material difference indicates exposure to different conditions. Difference in concentration of the base existence at lower and higher altitude could account for the 'GR' component. It is then difference in the material environment being compared; not a comparison of time passage in the same environment.