If you use just a 1 letter or number name for Link and Epona, does that save time with the text or not?

If you do a route that includes making a BiT Save at the very beginning, Link and Epona's names default to Link and Epona anyway, so it doesn't matter at all what you name them at the beginning since they get set to Link/Epona regardless.

If you are doing a route that does not include a BiT Save at the very beginning, you can set their name to whatever you want. I believe that every instance of using Link or Epona's name is "fast text" which can be mashed through completely regardless of length, so I don't believe it matters.

The only reason text language matters at all is for the handful of "slow text" that can't be mashed through, and as far as I can remember, none of those "slow text" boxes include Link or Epona's name.

EDIT (courtesy of information from Devil6Lair and Dragonbane0): In 100% there are two "slow text" boxes that use Epona's name. "Slow" text in TP is shown at 2 characters per frame, so this can lose, at most, 6 frames from name length. Incredibly minor but it does exist.