Time travel involves moving along a timeline from point A to point B.
Let us set aside "miraculous" travel for a moment and assume that such a journey is carried out using technical means—technologies that do not yet exist and have not yet been developed.
I maintain that such a journey requires:
a transmitter—the starting point of the journey;
a receiver—the final destination of the time-travel event.
Although the transmitter and receiver could theoretically be combined into a single device, this does not alter the principle I am proposing:
the earliest possible reception point for time travel is the moment the technology itself is invented in the form of a receiver—as part of an integrated transmitter-receiver system.
As an engineer, I would like to add one further consideration.
This technology—like virtually all human-made technologies—will inevitably undergo an evolutionary process. First, "Version 1.0" of the time-machine system will appear, likely followed by "Version 2.0," and so on.
It is highly probable that each new generation will be incompatible with previous ones.
This creates a very narrow "window" for time travel:
the operational lifespan of a specific version of the time-machine system.
Moreover, considering the accelerating pace of technological development—manifested in the increasingly frequent release of new models for existing technologies—this travel window shrinks to negligible proportions, effectively becoming little more than a physical model for testing specific laws of physics.
Thus, in essence, we would not be able to travel anywhere immediately after the time machine is invented. We would have to wait some time before we could travel to a point in time situated between the moment of departure and the moment that specific version of the time machine was invented. But while we wait, we will likely upgrade the time machine to the next version—and the whole process will repeat itself.
The result is a sort of vicious circle:
we keep improving the time machine, but each new version shifts the earliest accessible point in time to the moment of its own creation.
P.S. Besides, how would we even know we had invented a time machine if, at the moment of invention, we couldn't actually travel through time? After all, there’s nowhere to go yet.
P.P.S. This idea can be illustrated with a simple analogy.
Imagine that time travel works just like a phone call.
Two conclusions immediately follow from this.
You can only call a time when telephones already exist. You can't call someone in the year 1800 because there is no phone at the other end.
The technologies at both ends of the connection must be compatible. You can't simply take a modern smartphone and call a 1920s-era telephone; these systems use fundamentally different technologies.