I can respond one of two ways. "Just go with it, mang!"
Pretty much my feelings on the subject.
However, a specialist in time machines might not have studied as much detail about History as you'd think. He probably goes to archeologists, historians, and anthropologists if he wants to get detail on how to calibrate his equipment. But knowing how to put together temporal translocation equipment doesn't mean you know intimately the events the equipment can translocate to.
He might not even be interested. I've known more than a few scientists and engineers who were very single minded in pursuing a goal. Sometimes to the extent that the dullards controlling the purse strings were surprised and occasionally, if their IQ's are at least three digits, scared spitless by what smart men driven by a need to known and to build can deliver.
Been there myself a time or two.
Regarding calibration. I can see that historians or archaeologist could provide a general time frame for a particular window on the past. However, that only gets me in the ball park so to speak. To calibrate a time machine I'd want to use events I could date accurately and precisely. A historian can tell me that a particular view looks like first century Palestine but an astronomer can tell me that a total solar eclipse occurred at 25 o
27.9' N, 50 o
53.6' E on Nov 24, 0029 AD at 09:24:57 UTC.
In truth I think the details of calibrating a time machine involve not just time but also space. In fact it is spacetime -- the whole thing -- that provides the coordinate system. This is something most time travel stories miss completely. OTOH, this story is not really about time travel anyways so I'll suspend my disbelief about that aspect and see how the story comes out.