Mark 13:19 For in those days shall be affliction, such as was not from the beginning of the creation which God created unto this time, neither shall be.... where the exact same expression is used, and again has clear reference to a temporal framework inaugurated by God's act of creation.
If one accepts the Markan record as theopneustos (God-breathed), then we need not worry about the overlay of the hebrew, because only part of the statement is from Genesis. the remainder is Jesus’ own direct teaching
The Markan passage that you cite does nothing for the young-earth theory, even if it can be demonstrated that the term refers clearly to temporal rather than logical ordering. “Old Earthers” can still hold for creation in time. I’d be interested in substantial scholarly support (meaning a solid discussion of the linguistic evidence, not a list of scholars) to your claim that this term had an established technical meaning, but unless this meaning is both crystal clear and it can be shown that the phrase was only used with regards to the technical meaning, the linguistic difficulties, while not a completely “safe haven” to definitively end the argument, are considerable and cannot be brushed aside.