That time-travel trick was a great idea. It solved an ever-present problem in erotic fiction:
As a writer, you want to show events from the protagonist's view-point, and describe their inner experiences, but that point-of-view prevents legitimate use of the kind of external description that the reader needs to clearly visualize the situation.This lingering difficulty tends to result in:
a) head-hopping
b) point-of-view violations where the protagonist is magically able to see things they couldn't possible see
c) a peculiar excess of convenient mirrors and reflective surfaces
d) the 'camera' cliche, where a camera feed of the scene is fed back to the protagonist
e) re-telling the scene again from another character's point of view
The viewer-only time-travel is a neat way around it, though would probably lose its appeal if over used.
It's also problematic, in that it
can raise questions in the reader as to what else might be viewed this way, and wasn't, and why not?
In a longer story, it would probably lead to such questions. Another down-side, is that it can confuse readers who are simply skimming, and looking for the sexy bits. This wasn't likely to be a problem in this case, as it was all sexy
I believe this device
has been used before, but not often. I think past uses were also more plot heavy, and less about a straight-forward point-of-view device.