##In that particular example sentence, no. In general, yes.

The circumflex used by some authors to indicate long vowels. I prefer to use the macron: *hōra* versus *hōrā*. Some ancient inscriptions used an "apex", a diacritic similar to the modern acute: *hórá*.

*Hōra* with a short *a* is unambiguously nominative, "a time" or "an hour". While *hōrā* with a long *a* is unambiguously ablative, "at the time" or "in an hour".

In your example sentence, it's unambiguous that the word is *hōrā*, because *hōra* with a short *a* wouldn't make sense. So even without any markings, it would be read with a long *ā*.

But there are other situations in which long and short vowels can cause significant ambiguity. For example, a famous graffito (paraphrased):

> *A. B. amat, sed B. alium amat*  
> A. loves B., but B. loves *alium*

In this case, the ambiguity is used for humor: *alium* with a short *a* means "another man", but *ālium* with a long *ā* means "garlic".

Or for a more risqué example:

> *C. anum amat*  
> C. loves an *anus*

*Anus* with a short *a* (feminine, fourth declension) means "old woman", while *ānus* with a long *ā* (masculine, second declension) means the same thing it does in English.