It refers to the amount of time that a Hispanic, particularly Spanish people, say they'll be somewhere and the time they are there. If you're gonna meet them at 16:00, the interval is from 16:20 to 18:30 usually, but be sure that they'll show up at least 20min late, i've lived in Spain for 18 years now and I can swear it's always like that.
(this is a real conversation I had with a Spanish friend)
him- Why are you mad at me now?
me- is your fuckin' watch broken or what? you said you were going to come at nine and it's ten!
him- I'm not late enough! I'd maybe be late if I had shown up at twelve.