I always enjoy comic strips that step outside their allotted spaces to make fun of comic conventions. In this case, two very different comic strips offered humor based on comic strip pacing.
The first comes from a sequence of Barney & Clyde originally published 4/18/17. This smartly-written (and drawn) strip by Gene Weingarten, Dan Weingarten, and David Clark has a long history of playing with comic strip conventions.
The second comes from the 2/5/17 Sunday edition of Beetle Bailey. From the outset, Mort Walker's strip was always a simple gag-a-day comic. Over the years, the strip has grown a little, though still within comfortable boundaries.
In both cases, the punchline arrives in the last panel -- which is also an integral part of the joke. It's interesting to me to see how the two creative teams handled the same concept. In Barney & Clyde, the punchline "you'll never know when you're in life's fourth panel" is humorous because, well, that's where it is.
At the same time, it's left unclear as to whether Cynthia and her teacher are aware that they're in a comic strip. That ambiguity also gives the line a little more weight.
I felt differently about Beetle Baily's take. There's nothing wrong with the joke itself, and it's certainly true. Comic strip (and animated characters) often hang in the air for an unrealistically long time for comic effect.
And yet, to me, this sequence just seems lazy. I suspect that if there had been an additional panel or two to fill, we would have seen Sarge and Beetle hang in the air even longer. I guess the difference is that Barney & Clyde use the observation to base the punchline one, while Beetle Bailey lets the observation be the punchline.