The purpose of hyphens and dashes and, indeed, virtually all punctuation and other printing conventions is not generally to add meaning but rather to make parsing the existing meaning faster, easier, and/or more pleasant.
So you could write
I am expecting to fill two interview slots—one from 12:30–1:00 p.m. and another from 2:30–3:00 p.m.—for the secretary-treasurer position.
using all one symbol:
I am expecting to fill two interview slots-one from 12:30-1:00 p.m. and another from 2:30-3:00 p.m.-for the secretary-treasurer position.
But the former is, to me, at least a little bit easier on the eyes and a little bit easier to comprehend on the first pass.
Note that even conventions like different cases of letters, or spaces between words, are not an inherent feature of written language (see Wikipedia). Obviously, even the second sentence above is significantly easier to understand than
but even that can be deciphered based on contextual clues.
Of course, there are a myriad of other printing conventions that professional typesetters use to make reading a more seamless and enjoyable experience, that we don't attempt to duplicate in everyday communications (for example, customized kerning, or adjusting the space between letters, just to name one of the most basic). And it is possible to make substitutions for most dashes and hyphens; this is largely a matter of style and personal preference. For example:
I am expecting to fill two interview slots (one from twelve-thirty to one in the afternoon, and another from two-thirty to three) for the combined secretary and treasurer position.
However, most of us would like the option to use some aspects of the first example, so hyphens and dashes are probably not going away anytime soon.
Bottom line, if the extra keystrokes required for various dashes is really bothersome to you, you can leave them out; you can either use extra hyphens to approximate them, or substitute other punctuation or extra words to clarify your meaning (or live with the possibility of ambiguity and re-reading on the part of your audience). However, keeping them in your writing toolbox will give you more options for writing sentences clearly and concisely.