Do speakers take time to warm up?

b_limo, my understanding is that the speaker drivers have an initial "break in" but is very short duration at the factory, and perhaps somewhat more over the initial period of use, more on the order of first few dozen hours, not continually as if reverting back to an initial state.

My guess is that any "loosening up" would be in the first second or two upon using them. How is a person supposed to determine from listening that any kind of loosening up has happened when human hearing is not as consistent as electronics? Forget about it, as it's a waste of your time. Put your time/money into getting better gear.

I move speakers in and out continually, and I pay no attention to such things. To do so would be a waste of time for me and lead to far less productive system building.

I don't know that your caps are charged even if you leave the amp on. No signal to the speakers.

Work on the major things that make improvements, not the cheap, low grade things. Do not settle for insipid, low productivity changes.

How about tube degradation? Why not worry that leaving your tube amp on is slowly degrading your sound via shortened tube life? Is the benefit of speaker "warm up" overcoming the degradation of tube wear? See what I mean? Forget the nonsense, and work to achieve vastly superior sound with a better system. Save your money, get better. Forget the junk methods. An audiophile can waste their life in pursuit of questionable activities instead of going after far better experiences. Don't be someone who wasted 20 years on the inconsequential stuff as opposed to getting a grand system.

The original poster makes an observation about the phenomenon of speaker warmup, and your advice is to forget all this nonsense and buy a better system?

Why not just play music and accept that for the first half an hour or so it isn’t going to sound the best? A much more cost effective solution I think. What all this has to do with tube life is beyond me.

same observation as pesky_wabbit has made.
half an hour makes all the difference.
this is with Nautilus 802 first gen, of course well broken in after 20 years.
and after only a day pausing.

I understand your question in two parts:
a) do others hear the same and
b) if yes, why?
a) I hear the same, starting with and a long time with Maggies. The "simpler" ones had film caps, so no "real" cap forming was involved, and the degree of this speaker break-in is more and different from what I ever heard in caps & electronics. The Maggies sounded thin before "moving", my actual ribbon hybrids (dynamic bass to 400Hz) sound somewhat murky or "cloudy" when off for a certain time.
Leaving the system off for eg. 10 days necessitates several hours of gymnastics, the more the better.
b) as to why: I suspect the murkiness of dynamic drivers ( :-) improve a lot with gymnastics - but think about the damping, the mechanical hysteresis of the spider and surround, and even the membranes...
Interestingly Maggies, that have almost no damping, providing sort of a "clean spring" within the thin mylar foil, improve. Here it's probably a slight relaxation of that spring, probably affecting all planar speakers - ... including the newer plastic foil based Heil AMT drivers...?
Additionnaly to this there is probably a certain kind of static build up of magnetic remanence within generators, pole pieces,  traces of magnetic metals in contacts (nickel) and contact supports. This is probably kind of ho-hum demagnetized by music signals.
And moving a speaker (or other audio gear) from one place to another kind of takes time and energy to adjust.
In short: I hear the same and just don't listen too focused for several hours of reconnecting a system (instead: keep on playing music in a gapless mode... :-)

I experience the same, non scientific, thing. Speakers sound a bit better after a couple of songs are played. Even when the system has been on a while. 
The same with guitars. If a guitar hasn’t been played for a while, it takes a bit to open back up. 
Museums have musicians in to play the Stradivari violins. 
Instruments need to be played.