A. The armoring of Farmer Giles. Why is so much time spent on describing
this?
For the same reason a big fuss was made of it in "Cat Ballou": it's funny (all
the time spent on those rusty links to make mail), because it's so out of
character for this rustic farmer (not to mention the smith and others
helping). We think little of a real knight suiting up (although it can be
dramatic, as with Theoden and Aragorn before Helm's Deep in the movie), but
watching someone donning armor that is totally alien to him is something else.
B. Dates. Why does Tolkien specifically date the tale by the Christian
calendar days like Christmas, Epiphany, etc.?
Because the Little Kingdom is visualized in a hypothetical medieval Europe,
which based its social rhythms on these church dates. Hey, they have a
parson, after all! After all, Tolkien's choices are (a) to use "real"
dates like March 25, which is a little cold, (b) invent a fictitious calendar,
which is distancing, or stick with the medieval
allusions.
The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people are so full of doubts.-- Bertrand Russell