...when they dropped the two-episodes per plot (and the inevitable cliffhanger ending of episode 1) in favor of the single episode format.
Amazing how I still hear the catchphrase "Same bat-time, same bat-channel" decades later, in reference to a recurring event or such. I even use the line myself sometimes.
Wasn't there at least one cliffhanger that the dynamic duo had no real way of getting out of? And when they returned the next day, they
already had escaped, with one of them beginning with something like "Can't believe how we got out of
that one, Batman!"