Newton, in the Principia, conceived time as flowing everywhere at the same rate (this was anticipated also in Aristotle's Physics).
Time here is independent of bodies and particles. In a sense it is external to them.
Einstein introduced a conception of time in which a 'clock' was carried by a particle - or 'proper time'.
Is this consonant with the Kantian notion that time is a synthetic and a priori notion? Of course, an immediate distinction is that Kant had in mind the experiential reality of a mind. Whereas a particle in this sense does not, but in another sense it may as it 'experiences' force.