Ancient India (at the time of the Buddha) used a calendaring system called “lunisolar”, which is of course much different than our current way of calculating time and date. The Buddha did not invent his own calendaring system, instead just deferring to the default system that was in use. Ethnic Buddhist countries later adopted a lunisolar calendaring system (in the 16th Century), originating by and large from the Greeks. I talked about that system recently here.
Sure, in Buddhist countries, the Buddhist year might be reckoned as 2561. But look at your computing device right now: what time and date is it in the corner of your screen? My laptop informs me that it’s Monday, April 16, 2018. It couldn’t care less about the lunisolar calendar. Just like whatever computing device you are also using.
Our computing devices all use a time-syncronization protocol called NTP. This makes your computer’s system time accurate to well within a tenth of a second. It’s actually pretty cool, and severely punts the bottocks of the lunisolar calendar in the way of technical accuracy.
Due to it’s effectively global scope (who doesn’t have at least a smartphone these days? Pretty much nobody?) I would argue that NTP (which syncs your computer’s clock to UTC) could be called the only calendaring system which actually matters any longer.
It’s mind boggling to think that in our lifetime, as in like within 10 years ago, all the multitudes of ways to keep time were pretty much “all sorted out”, once and for all, in the sense that virtually everyone has a smartphone now (if not also a tablet, laptop or desktop), and that smartphone, etc. will synchronise itself to UTC (via NTP).
In summary, I pretty much don’t care what wierd culture you are from, your computing device, which most people probably use to check the time, day-to-day, and which most people’s faces are pretty much glued to now, day in and day out, now syncronizes itself to UTC, using NTP (and you simply specify what timezone you are in).
Sure, you can install an app to show you dawn, solar noon, and the full moon, etc, but the OS does not run according to those, or care, or show the system time that way. And virtually all apps you use all the time, show times by way of UTC (including this forum), as they all look to the system time as authoritative.
PS: UTC timezones look like this (which you probably already know):