The last time 'Pac was in the studio was before the MTV VMAs when the whole beef with Nas came to a head, so even if you believe that the two of them made peace (which I don't), he couldn't have recorded this song after the VMAs.
Timeline:
July 2nd, 1996 - It was Written is released
July 4th, 1996 - House of Blues Concert
July 5th, 1996 (or a day or two later), - 2Pac freestyles over the untouchable beat talking about the incident of Fatal pissing at the house of blues (at least i think that's what it was). The freestyle sounds like an incomplete version of the song, as if he's still coming up with the verses. Kadafi probably does his freestyle at this time also (Medicate)
^^The same day or maybe a day after the freestyle - 2Pac and Outlawz actually record the song, with the "no offense" line about Nas, probably using him because his album was just released and they liked Illmatic.
A day or two after recording untouchable, 'Pac and the 'Lawz buy It Was Written to see how Nas actually followed up Illmatic. I doubt they would have bought it the day it came out just because they were busy celebrating with Snoop getting out of jail and all. But they probably bought it now. Then they see Mobb Deep on quite a few tracks, and on top of it, they hear "The Message." With a little bit of pushing from Suge they decide it is time to get Nas involved in the East-West thing also. And you can probably figure out the rest.
Keep in mind this could all have reasonably happened within the same week.