For example, is there a semantic difference between the two following sentences?

Lapis descendit ab A ad B unâ horâ.

vs.

Lapis descendit ab A ad B una hora.

This site, e.g., says

The distinction between short and long vowels was grammatically significant, cf. hora hour vs. horâ at (this) hour, now

Is this true?

For example, is there a semantic difference between the two following sentences?

Lapis descendit ab A ad B unâ horâ.

vs.

Lapis descendit ab A ad B una hora.

This site, e.g., says

The distinction between short and long vowels was grammatically significant, cf. hora hour vs. horâ at (this) hour, now

Is this true?

For example, is there a semantic difference between the two following sentences?

Lapis descendit ab A ad B unâ horâ.

vs.

Lapis descendit ab A ad B una hora.

For example, is there a semantic difference between the two following sentences?

Lapis descendit ab A ad B unâ horâ.

vs.

Lapis descendit ab A ad B una hora.

This site, e.g., says

The distinction between short and long vowels was grammatically significant, cf. hora hour vs. horâ at (this) hour, now

Is this true?