This is the 1909th most frequent Spanish word.
once
"Once" means "eleven" in English.
In this sentence, 'once' is used as a numeral, specifically the number eleven.
Yo tenía once años cuando aprendí a nadar.
I was eleven years old when I learned to swim.
Here, 'once' again functions as a numeral, describing a time quantity — eleven minutes.
Me atraganté justo once minutos después de empezar a comer.
I choked exactly eleven minutes after starting to eat.
In this example, 'once' is used to denote the time (11 o'clock) in hours.