This is the context:
Finally, I would say that, even within physics, philosophers are sort of like theoretical physicists, and physicists are like experimental physicists. Experimental physicists don’t like theoretical physicists, because what are the latter really doing?— a lot of mathematical noodling, and they don’t really work at all. The experimentalists instead think they are getting results. The joke experimental physicists say is, “Theoretical physicists will never schedule a meeting on Wednesday because it spoils two weekends."
Source: The origins of the universe: why is there something rather than nothing? (in the Annals of The New York Academy Of Sciences)
Can anyone explain this joke?