I can basically pick and choose whatever I want in terms of what's in the setting and what's not. You should have a fairly loose sense of an aesthetic for what there is. Rifles exist, but are single-shot; muskets are more common; there's no multi-shot weapons; there's skyscraper cities; there's no cars, but magical beasts of burden for wagons work just as well, trains might soon become a form of transportation, an expensive spell for instant transportation is runic return, and so on and so forth.
And it being a fictional world. Its dates aren't going to correspond to ours.
And that's what I worked on. In our world, we've got 6,000-7,000 years' worth of recorded history, loosely speaking. And I decided I might as well steal from that:
The setting of Phyrra and Cyrus begins in the year 6829 LC. LC being what you can think of as equivalent to combining AD and BC: The start of that calendar's usage, which coincides with the start of recorded history. WE have that shifted into BC and AD because...well, no real good reason actually, just because, pretty much. This is a calendar more or less just removing the unnecessary break, more or less.
I haven't really put much detail into it beyond that, but hey, give me some credit here, I'm literally writing this as I go to bed.