Does the blessing given at Genesis 1:28, have anything to do with why Jehovah did not immediately intervene to prevent the spread of disobedience, after Adam's sin?

Good answers, so far.  'Free will' was an important factor, yes, without question.

Here is an additional factor, that Jehovah had to consider:

"Further, God blessed them, and God said to them: “Be fruitful and become many, fill the earth and subdue it...And it was so."- Genesis 1:28-30

The word "blessed" indicates that Jehovah granted "them" a 'right'- or 'charter'- 'promise'- along with His direction.

And Jehovah always keeps His promises!

If the "serpent"- (and we know who that is)- had acted prior to the blessing, Jehovah would not consider Himself bound by His own word.  If the "serpent" had acted 'after' the human couple had produced offspring, those that were alive, yet still obedient and righteous, could have been given Adam's right of responsibility and authority, and Adam and his wife, could have been disciplined 'apart' from their action's effect on mankind as a whole.

Thus, the "serpent" shrewdly chose the
precise moment to act, to effectively create a conflict of divine
pronouncement, which would result in the sudden existence of a domain that was 'outside'
of God's authority- he thought- where he could freely act.

Aware that Jehovah will remain true to Himself, and not break his word, the "serpent" schemed to use this fact against God, deciding that he had the opportunity to take advantage of Jehovah's good intentions toward His creation.

So 'free will' became the "serpent's" toy (or 'tool'), and the Earth a place beyond the immediate authority- even from Jehovah's own point of view- of God's direct rule and swift justice.

But, of course, Jehovah still maintained that His creation belonged to Him alone, and that He was rightful ruler over it, and would reassert that divine right, once He acted to reverse certain 'effects', created by the 'cause'.

Yes, then, a great deal more than the simple act of reaching for an unauthorized piece of fruit, was taking place, when Adam 'derailed' his human family's future.  Jehovah would not have permitted such atrocity and suffering to commence, unless extreme reasons were involved!

Some of those 'reasons', we may not even be aware of, yet.