When will 70 AD happen?

 'Do you see these great buildings?' replied Jesus  [referring back to the discples comment in Mark 13:1]
'Not one stone here will be left on another; everyone will be thrown down.' Mark 13:2

This is a very helpful analysis of this chapter by France:

v2	(No time indicator in prediction)
v4	WHEN?	(and what will be the sign..?)
		v5 Watch Out - it is NOT YET (v7b)
			v8 all this is only the BEGINNING
		v9 Watch Out - it is NOT YET
			v10 gospel to all nations FIRST
			v13 the ‘end’ still in the future
	v 14 But when	i.e., as opposed to the NOT YET of v5-13, here the sequence begins (in ‘those days’, v19)
		v21 At that time    this is not the end
		v23 Watch out     still beware of assuming too much
	v 24 But in those days              following that distress		reference back  to v19 -
	so a direct, unbroken sequence from the when of v14.
v 26	And then	Here at last is the answer to When? v4
v 27	And then
	v 28f The fig tree (a parable of necessary chronological sequence) shows that these things indicate that ‘it is near’
	v30f and therefore all these things must inevitably occur within ‘this generation’.
v 32	But about THAT day or hour ...
	WHICH day or hour? - no (singular) day or hour so far mentioned
	v 33 Watch out - it may be ANY time
	v 32-37 speak throughout of an UNKNOWN time, which comes without announcement, in stark contrast to the
		NOT YET BUT WHEN THEN WITHIN GENERATION	of vv 5-31

Divine Government: God's Kingship in the Gospel of Mark p128