:)   Please note that often in scripture when the 40 years is mentioned,  the judgment happens a year or so LATER beyond the 40 years !!!!
As far as I can see, GOD, being merciful, does give space to repent.....  judgment comes upon the NEXT generation......
for example what GOD said to Solomon  and  Josiah........ Israel has been given 40 years to repent since 1967, so we can clearly see that this is a similar case in point; and that the judgment is coming just beyond the 40 years........upon the next generation
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Now as to the case of the judgment of  the generation killing Jesus, Jesus said that it would be LESS THAN 40 years; coming upon THAT Generation.......  HE was killed about 33 AD,,, Jerusalem was destroyed in 70 AD, or 3 years shy of 40 years........

Another Case in point, Israel wandered in the desert 40 years just as Israel has wandered 40 years in unbelief...... AFTER the 40 years were over the NEXT generation entered the promised land......
 
Lewis  Brackett