1 January 1970

The internet became pervasive in the mid 90s, and "always on" cable internet started to be widely available in the late 90s. Cell phones became pervasive around 2000-2001, Facebook hit big with colleges in 2004, but the iPhone release in 2007 changed everything. Within five years, almost everyone in the developed world had a smartphone, and had instant access to the entire internet, a built-in camera, and were always available via call, text, email, chat, or social media, with an endless stream of apps.

2012 is my vote, that's when the majority of the developed world had adopted "always on" technology that still stresses us out today.

It scaled with venture capital and technically it all started with William Shockley https://en.wikipedia.org/wiki/Shockley_Semiconductor_Laboratory

The story goes that the USA never ended the military industrial complex after WW2 like real ethical people. The problem is how hard it is to have radical projects that do not get wrecked by partisan politics. The solution was to put cutting edge military research as far from Washington as possible. This is what created silicon valley initially. Shockley was at the cutting edge of semiconductors, and it was through him that the realisation was made that a venture capital based economy was a possible transition away from a military spending based economy. Everything that has come after is the steamroller of venture capital. It has moved deeper and deeper into all aspects of life but it is all centered around semiconductors. Bleeding edge fabs are the most extensive operations in all of human history. They are the cornerstone of venture capital. We are reaching the end of what is possible in the silicon technology and that is a problem. It all scales so that as we move forward the products get cheaper and cheaper with each new node in the fabs. As the fabs move forward, so does everything else in the periphery. Growth requires forcing people to spend lots of money and take big risks. That growth really took off in the late 00's and early 10's for many reasons. Capacitive touch screen technology, and cheap flash memory were the most impactful IMO. Still, the ball started rolling slowly with Shockley.

It's a process, that's like asking when did we get to the modern medicine, was it germ theory? Was it antibiotics? It's a process, it's hard to pinpoint the moment something becomes "modern".

For me I think I would put it around 2013, that's when I got my first Android phone, I had a Nokia n9 before, so not my first smartphone, but around that time as well data on mobile became more accessible to me. With the N9 I would use the wireless on most places and my data just to check emails or something, but around 2013 I started to use data more and more on the phone itself, and started to think with the always on mentality that I think it's a staple of what you're describing.

By 2013 I also had social media, watched YouTube, and video calls had become more common place (even though video calls were a thing long before then it wasn't that common, not everyone had a webcam).

That being said some friends of mine got into that bandwagon way earlier, I remember a friend being a huge Android advocate back in 2010, he was always online even before I got my first touch screen phone (I even remember being concerned about the lack of physical buttons). While other friend got her first smartphone in 2014, and the always on mentality didn't came until much later for her, possibly only by 2016 or so (she used to complain that I checked in on Foursquare to get free things). So it's a process, and possibly it happened at different times for different people, but I think it's fair to say that it wasn't very common before 2010 and it was almost ubiquitous in 2018.

Note: I lived in Brazil during that time, I also saw a shift in the delay we got new technologies, before it took months or years to get new stuff, bit later you could get the latest phone on any store. Again, this was a process so it's hard to tell you when it happened, but definitely Brazil from 2000s was a lot more delayed in getting new technologies than Brazil in the 2010s

Defining technology shifts by presidential terms doesn't work... Trump gained his following on social media like Twitter while Obama was president (so before 2016).