Say you go into a Sherwin-Williams or Lowes or whatever and pick out a color and order a couple of cans. How long do they take before it’s ready?
Five minutes maybe? Ten? It’s not very long.
C’mon Pork. This here’s the Dope. The answer is a mean of 7.89 minutes (SD .5 minutes). The median time, however, is 5.65 minutes, indicating a longer right tail of the distribution curve, which I hypothize may be related to a linear arrangrment of other customers waiting for their turn to get their paint mixed. However, whether the analysis controls for one being in Sherwin Williams or Lowes is not clarified in the paper I consulted.
Every place where I have bought paint has had an automatic mixing machine. They start with white paint, add in the colors in the amount needed to make whatever color you want, then put the cans in the machine. The machine shakes the bejezus out of the cans for a few minutes, and it’s done.
Maybe ten minutes tops for the entire procedure.
Since the OP may be asking about the time to have custom colors prepared then it’s just seconds to prepare the mix. They’ll take a white or clear base and add measured amounts of pigment from a dispensing machine, then put the can in the shaker for 7.89 minutes as described above.
OK. I was really just curious whether it was a “stand there and wait” kind of thing, a “go run some other errands and come back in an hour” kind of thing, or a “place your order and we’ll call you when it’s ready next week” kind of thing.
Yes, you can stand there and wait or go back to the shelves and check if there is anything you forgot (amazingly enough according to a recent thread here Dopers fail to analyze a project completely or are forgetful and almost always have to go back to the store).
CITE???
Of course there is a nonzero chance that all that agitation will rearrange the paint base and pigments back into their unmixed starting positions.
Not with a homogeneous mixture 
I think that’s still talking about probabilities, just not explicitly. The enormously likely outccome oo randomness on a homogenous mixture is that it stays mixed. The infinitesimally small (but nonzero) probability is that the randomness * just happens * to unmix it. Possibly so unlikely that a whole universe of shaking paint cans would end before it probably happened.
Also, there’s a nonzero chance that the sum of quantum flutuatios etc in that region of space cause the pigments to spontaneously jump out of the can, or the whole thing disappear and be replaced by a banana.
It could take longer if the place is busy. My home depot tends to take up to half an hour because there is just one guy at the counter.
Based on observation, as opposed to participation, it appears that waiting times for paint mixing are longer on Saturday mornings than on week days. 
Yeah…I switched to Sherwin-Williams, mostly because the painter my GC used wanted to use them. Happy side effects:
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Shorter lines. They have enough mixers to handle a few orders at once, and I’ve never had more than one person in line ahead of me.
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They have a nice record of all the colors I need for my house. I typically know them anyway, but it’s a good off-site backup.
This info is pretty dated, I admit.
In college, I worked in the paint department of Montgomery Ward from 1981-84. No automation at all. I was one of the maybe 25% of the staff that were good at mixing paint. The others were too slow, or made too many mistakes. I also repaired the mixers and colorant dispensers.
We had several paint shakers, and the old reciprocating ones took about 5 minutes to mix a gallon. The newer “gyro-mixers” took about 20-30 seconds. The new ones spun the can on two different axis at the same time. The newer ones got heavy use, and it was not uncommon for them to break down. Weekends in the spring we would have 3-4 people mixing paint, and all available shakers running with paint queued, and staff queuing for the two colorant dispensers.
Assuming a gyro-mixer was available. To mix one gallon (or quart) was usually about 2 minutes for the first one. A lot of that was walking back and to the stock room where we kept the mixing equipment, and about 30 seconds to find the recipe in the book.
In my prime I could often keep two of the new mixers running pretty steady on a large order, so about 15-20 seconds per gallon. That was for a simple recipe with only 2-3 different colorants added. I recall mixing a 16 gallon order in 5 minutes once, just to see if I could.
But there could be delays. You had to keep your ears open for the slurping noise when the colorant dispensers ran low…and then you had to stop, shake a can of colorant, and top up the reservoir. The colorant was added to “color base”, not white as everyone assumes, and I might have to fetch it from a second floor stock room.
From what I have seen, the new electronically controlled colorant dispensers are mostly about removing most of the need for skill and training, and aren’t much faster than I could do it by hand. The bulk of the time is still in the shaking, and the shakers are still a bottle neck when the place is busy.
I remember that as the highlight of going to the hardware store with my dad!
Wouldn’t it just come back in three days?
Paint joke!!
My apologies - I forgot to check back in. Here you go
Definitely closer to 10 minutes. If you go in there on a Saturday morning it will take longer, but a weeknight should be fast.