To come to pass: take place —used in the subjunctive with inverted
subject and verb to express the particular time or occasion
Come spring the days will be longer. m-w
Preceding a future date, time, or event. When or by the time the
specified date or event arrives or takes place; at or by the specified
We'll be married eighteen years come next Tuesday. OED
... and we would be disposing of Doctor Millions' cow herd,
consequently there would be only enough work for Albert and Stretch
come next winter. Baxter Keith; The Judas Kiss
Often used with expressions: come what may, come rain or shine, etc.
Come hell or high water—whatever the obstacles. E.g., Come hell or high water, I am determined to succeed. I am anxious to succeed.
Rebecca Vorsah; General Knowledge of English Literature
...Daniel's vision shows that regardless of a person's power, might or
control in this world, in the end, come judgement day, people will
find out who really is in control and will receive their just rewards.
Brian Curtis; Bits and Pieces 2018