Rebuild Post-Apocalypse

Ok, I’m not looking for likes, just thoughts & answers:

So.

After an apocalypse, how long does it take to rebuild society and “modern” structures given:

a) a hidden magic world in which the magic society is largely unaffected,

b) the apocalypse is caused by a surge of magic that harms tech (steam level and earlier still works),

c) magic can be used to replace tech for communications, travel, and such.

Thoughts?