1. The Russo era in late 96 was when I really recall it becoming a thing, because that's when the new format of the 20 minute interview to open the show became in vogue, which would then set up a main event that the show built towards. Say what you will about Russo, but he tended to put together shows that were more in the traditional format of wrestling booking with minor things to open, leading to bigger things at the end.
2. Yeah, following from #1, the previous format was the same one set out by the SNME formula, where it seems like Vince got heavily influenced by the TV side of things and front-loaded the shows. Especially once Nitro started cutting into the ratings, it became really important to hook viewers and get them to stay for the duration of the show, and that is one aspect where I don't think Russo gets the credit he might actually deserve. The Wars really did change the format of wrestling completely.