I'll elaborate my question

This is 2nd verse of Jingle bells sung by Jim Reeves.

Now the ground is white
So, go it while you're young,
Take the girls tonight
And sing this sleighing song;
Just get a bob-tailed bay
[two-forty as his speed]
Hitch him to an open sleigh
And crack! you'll take the lead.

In the bracketed wording above, what does two-forty mean? Is it 240 miles for a horse speed? What did the orginal writer have in mind when he wrote this?

Please enlighten me.