The idea used by Ethel Wilson -- of Time as an efficient cause -- is not simply a fictional conceit. In contemporary Western society, Time is assumed thoughtlessly to be what a clock does: a rigid linear series of equal units. This was not the experience or understanding of time, certainly, in the pre-modern West, and likely not either in non-Western cultures.
The lecture thesis on Ethel Wilson is that she is the first post-modern writer. Innocent Traveller certainly, as I read it, is in sympathy with Albert Einstein's relativity theory (again, as far as this layman understands it!)
e = mc2 (energy equals mass multiplied by the square of the speed of light) is an equation that represents matter as being energy at a particular speed. For students of fiction this has as one important implication that the thoughts and actions of characters -- i.e. forms of energy -- have real and significant effects on the material world and on the movement of history, making the writing, reading and academic study of fictional representations of life a worthy enterprise.
Of interest to our understanding of Wilson's fiction is the fact that Einstein's famous equation also defines Time as being Matter and Energy in a certain relation. Reformulate e = mc2 as c = [root] e/m.
Reading this formula in a fictional way, then: if we read Wilson's novel as representing the human spirit as energy (Topaz is obviously a personification of energy) and the circumstances of the world (marriages, emigrations, etc.) as matter (using "matter" in the colloquial British sense) then the depictions of Time that Wilson has woven throughout her narrative are to be read by us as having the same reality as matter and energy do in our ordinary understanding
By the way, with these formula, we're just having fun here: definitely no Math for the final exam!
But to continue with the exercise, to help understand how the "c" - speed of light - in Einstein's relativity equation relates to Time, just look at it this way.
Think of distance ("D") as being a change in place ("ΔP"). And Speed in general is represented as velocity ("V"). And of course Time is "T". You'll remember from High-School that the formula for velocity is V = ΔP / T. (Recall that we're saying that "D" is the same as "ΔP"). If we recast this equation for Time "T", then T = ΔP / V
So, if our velocity "V" is a particular value - using Einstein's speed of light "c" - then c = ΔP / T and T = ΔP /c.
Let's return to fiction! This last formulation lets us read Innocent Traveller (the traveller is the one ΔP'ing!) as showing us that Topaz's travels - to Vancouver, then to ... where? - and her velocity (Wilson depicts Topaz explictly as being nothing more than non-stop rapidity of speech!) are a form of Time. Or in other words, Topaz did have an effect on Time-with-a-capital-T: or, in the word the text uses at important points, on Eternity.
This, then, is what Rose/Ethel sets out to achieve through her narrative fiction - an eternal life for her Aunt Topaz/Eliza.
Physics, Mathematics, &c. experts more than encouraged to correct the forumlae.