Used in letters and reports, "instant" referred to a particular day in the same month.  For example, Robert E. Lee's Report Concerning the Attack at Harpers Ferry, written on October 19, 1859, states that Lee arrived on the "night of the 17th instant".  The "17th instant" would be October 17th. 

mid-15c., "now, present, of the moment, current," from Old French instant "near, imminent, immediate, at hand; urgent, assiduous" (14c.) and directly from Medieval Latin instantem [..]

late 14c., "moment in time, infinitely short space of time," from noun use of Old French instant "near, immediate, at hand; assiduous, urgent" (see instant (adj.)). Related: Instan [..]

instantaneous: occurring with no delay; "relief was instantaneous"; "instant gratification" blink of an eye: a very short time (as the time it takes [..]

n. A very brief portion of time.

in the Authorized Version, means urgent, urgently or fervently, as will be seen from the following passages: (Luke 7:4; 23:23; Acts 26:7; Romans 12:12)

herefayen

being under present consideration [the questions presented in the case]

(n) a very short time (as the time it takes the eye to blink or the heart to beat)(n) a particular point in time(adj) occurring with no delay(adj) in or of the present month(adj) demanding attention [..]

Process tea extract reconstituted with hot water

Instant cards have an immediate effect when played and are then put into the graveyard.

lang=en 1800s=1843 * '''1843''' — . ''''. *: And being, from the emotion he had undergone, or the fatigues of the day, or his glimpse of the Invisible World, or the dull conversation of the Ghost, [..]