"Una hora no es un instante."
Translation:An hour is not an instant.
"An hour" is correct in English as the "h" is not pronounced. For example, we say "a hospital" but "an hour." There are English speakers who will say "an hospital" and it is also correct but I "a hour" is not correct.
Typo error: It tells me, "an hour is not an instant". An comes before a vowel. "H" is not a vowel.