meaning of “come eleven a.m. or so”

Question

I'm reading The Fermented Man by Derek Dillinger. The author talks about his reaction towards sugary sweets after one year of eating very simply. It turns out the average amount of sugar most Americans put in their coffee tastes awfully sweet to him. Then he says:

I rediscovered the crash you feel from a sugar rush, an hour or two afterward, when you get nothing more substantial in your stomach. Coffee and a doughnut do not a good morning make, come eleven a.m. or so.

I’m very confused about the time references here, especially “come eleven a.m. or so”. What comes eleven a.m. or so? This part seems so fragmental and lacks its subject that I don’t know how to read it.

Is he saying something like… he had his breakfast (coffee and a doughnut) around nine a.m. and had sugar crash an hour or two afterward, which is around eleven a.m. ?

Answer 1

See this definition for come:

10. preposition
    You can use come before a date, time, or event to mean when that date, time, or event arrives. For example, you can say come the spring to mean 'when the spring arrives'.
    Come the election on the 20th of May, we will have to decide.
    He's going to be up there again come Sunday.

Answer 2

Your interpretation of what he means is correct.

"Comes XXX" where XXX is a time means "when that time arrives".

Answer 3

The "afterward" references the sugar rush.  In the author's experience, a sugar rush begins, and then there is a sugar crash an hour or two later. 

 

Feel free to consider "eleven a.m. or so" as the subject of a subordinate clause.  This subordinate clause is in the subjunctive mode, marked by the bare infinitive form of the verb preceding its subject.  In modern English it is more common to make such a clause subordinate by using a subordinating conjunction and leaving the clause in the indicative mode, as in "when eleven a.m. or so comes". 

There are a number of clichés that happen to preserve this old-fashioned structure: "come what may" and "come hell or high water" leap immediately to my mind.