Is it not the opposite? Rather than moving faster, more words are devoted to shorter increments of time.
> The average length of time represented in 250 words of fiction had been getting steadily shorter since the early eighteenth century.
Time passed per word has been decreasing. A page used to mean a week, now it means a day. In your horse vs plane example, this makes sense if they both gloss over it. EG "we rode 3 days to Rivendell" vs "I landed in Tokyo after a long flight".
> The average length of time represented in 250 words of fiction had been getting steadily shorter since the early eighteenth century.
Time passed per word has been decreasing. A page used to mean a week, now it means a day. In your horse vs plane example, this makes sense if they both gloss over it. EG "we rode 3 days to Rivendell" vs "I landed in Tokyo after a long flight".