It isn't so much a matter of "acclimating to the mended bone", assuming
that it was set straight, as the fact that the muscles and tendons will
have atrophied, and it takes a while to stretch them back to full length
and regain the lost strength in the muscles.  I both broke and sprained a
little finger once when I fell and tried to catch myself.  I wore a
plaster cast for two weeks, and a plastic splint (that could be removed
for washing) for another three weeks.  When the splint first came off, I
literally could not move the finger that had been immobilized.  I had to
go through about three weeks of stretching exercises, several times a day,
to get back the full range of mobility, and, 18 years later, I still have
times that the finger gets stiff and I have to do the stretching exercises
again.  Also, ever since the accident, if I relax my hand, the little
finger moves outward into the position in which it was set.  I have to use
my muscles to get it to move into line with the other fingers.

I mentioned, earlier in the thread, the family cat whose back leg was
broken by being run over, back when I was a child.  The cat eventually
regained the full use of his leg, but he still tended to stick the leg out
straight when he sat down.  Archer may well show the same behavior.