First, WOW!
That being said, sign me up on the list of folks who thought this was just the beginning. And it still could be, if you considered picking it up where you left off.
Always one to be the deserting voice, I actually like much of the lack of details. I like that it is not very specific where or when it occurs, which gives it a universal feel. Spartans, Teutonic Knights, Red Coats and GI Joes all had to hurry up and wait, some making it home and some not.
However, there were some clues, if unintentional, that leads me to believe this occurs post-Colombian era somewhere in the Americas, probably in the early 19th century. My guess is South America. My reasoning is that you mention tomatoes and potatoes, which are both 'New World' foods, and you mention he used an oven -- a pot on top of, not in the oven, which is a post-Industrial era concept. Also, the only weapons mentioned are a clash of steel on steel. This could be swords or possibly bayonets, so not too far into the gun powder era. Likewise, no pain killers are used on Darin -- in fact it was assumed there would be none with the leather tooth guard -- implying they weren't in common use yet. Lastly, your letter dates have months with vaguely Spanish names. I'm guessing you didn't intend any of this, but asses like me would catch that.
Page 5: The phrase "an extra day or three" has become somewhat cliched.
In the same paragraph you use "The ended up stilted, formal." The following paragraph you state "Well, they weren't bothering with the formalities..." In successive paragraphs this was a bit confusing. Perhaps change the second use to "ranks and files"?
Last paragraph, on first reading, I thought he had punched the fire place then cursed. Only afterwards did I realize he had thrown the letter into the flames.
All in all, nicely done. I'd like to read the rest of the story! *hint-hint*