Wild / hatched Pokemon CP is scaled on the level off the player but for eggs, will the scaling be done at the time I find the egg or at the time I hatch it.
It appears that an egg's CP is based on your level when you found the egg, not when it hatches. We currently only have anecdotal evidence for this, but there is quite a lot of it, which I'll list at the end.
However, eggs will never hatch pokemon above level 20. This was determined from reading the game's internal data files.
The following are sources of anecdotal evidence (from Reddit) supporting that it is based on your level when you find the egg. I have yet to find any posts about it not being based on when you find the egg.