The phrase time flies? you cannot: they go too fast and variants are punning extensions (in which time is a verb, and flies a noun) of the cliché time flies.
—Cf. also why is a mouse when it spins? because the higher the fewer.

These are the earliest occurrences that I have found, presented in chronological order:

1-: From the Children’s Column, published in the Burnley Express and Clitheroe Division Advertiser (Burnley, Lancashire, England):

– of Saturday 31^st December 1904:

Punctuate the following so as to make it read with sense:—
Time flies you cannot they fly in too irregular intervals.

– of Saturday 14^th January 1905:

The punctuation of the sentence should be, “Time flies! You cannot. They fly in too irregular intervals.” Or it might be, “Time, flies?” etc. The punctuation should be such as to express the idea of timing flies.

2-: From The Southern Daily Echo (Southampton, Hampshire, England) of Monday 16^th December 1907:

The trying sentence “that that is is that that is not is not is not that it it is,” is cleared thus by proper punctuation: That that is, is; that that is not, is not. Is not that it? It is.
It is difficult at first sight to grasp the meaning of this apparently simple sentence: “Time flies you cannot they pass at such irregular intervals.” How does it read?
Answer—“Time flies you cannot, they pass at such irregular intervals.”

(This was reprinted by the Brecon County Times (Brecon, Brecknockshire, Wales) on Friday 25^th December 1908, and by the Cornubian and Cornwall County Times (Redruth, Cornwall, England) on Thursday 23^rd December 1909.)

3-: From Our Children’s Circle. Chats, Acrostics, Puzzles, and Competitions, published in The Derbyshire Advertiser and North Staffordshire Journal (Derby, Derbyshire, England) of Friday 11^th August 1911:

What important things stops are! I mean commas, colons, semi-colons, full-stops, question marks, surprise marks, etc., etc. Here is a sentence from which they have been omitted. It is a sensible sentence, and reads quite right when the stops are properly inserted. What can you make of it?
“Time flies you cannot they fly too fast.”
I will leave the problem with you for a week, and then tell you how to read it. Those of you who learn English grammar may well try your hand at parsing the first two words.

(The answer was never provided.)

4-: From Amusements with Stops and Commas, published in Volume XVIII (1912) of The Book of Knowledge: The Children’s Encyclopædia (New York: The Grolier Society – London: The Educational Book Co.):

The little commas and full-stops, and other similar signs that we see scattered about this page, and the pages of all the books that we read, do not seem very important. Yet, without these, it would very often be quite impossible for us to know what a writer meant.
[…]
When a gentleman made the remark to his friend, “Time flies you cannot they pass too quickly” he was not talking about the passing of time, but about the timing of flies. A semicolon after cannot makes the sentence clear.

5-: From The Pawhuska Capital (Pawhuska, Oklahoma) of Thursday 22^nd October 1914:

“Time flies.” You can’t, they go too fast.
Figure it out,—have you caught it yet?

6-: From the Belfast News-Letter (Belfast, County Antrim, Ireland) of Thursday 3^rd June 1920:

CARNMONEY DROWNING CASE.
The Deceased Not Identified.

The City Coroner (Dr. James Graham) held an inquest in the Belfast Workhouse yesterday regarding the death of an unknown man whose body was found in Berry’s Dam, Carnmoney, on Sunday afternoon. The deceased was between 30 and 35 years of age, and was about 5ft. 10ins. in height. His hair was brown, and he wore a moustache. Sergeant Burke stated that the clothing of deceased “appeared to be that of a respectable man.” A slip of paper found on the body contained the following words:—“That that is, is; that that is not, is not; that is so. Time flies; you cannot then go so quickly.”

7-: From the Border Children’s Club, published in The Berwickshire News (Berwick-upon-Tweed, Northumberland, England) of Tuesday 26^th June 1923:

Can you make sense of this?
That that is is that that is not is not [is not] that it it is.
With the proper punctuation it is quite simple. The sentence should read: That that is, is; that that it is not, is not. Is not that it? It is.
Here’s another sentence that looks awkward; but it only needs commas.
“Time flies you cannot they pass at such irregular intervals.” It should read: “Time flies, you cannot, they pass at such irregular intervals.”

8-: From the Evening State Journal and Lincoln Daily News (Lincoln, Nebraska) of Tuesday 29^th November 1927:

FLIES ON THE WING.

“Time flies; you cannot—they go too fast,” was a time-honored catch phrase, until recently the United States bureau of entomology did that very thing. House flies, it found, often made a journey of five or six miles in twenty-four hours. Some 234,000 flies of different species were obtained for the unique flight tests, which were conducted in Texas.