"Give me a sec" refers to when a person is going somewhere but they have to finish something up. This gives me a second that could take up to 1 minute to 3 days.
Kirby:(texts Joshua) When are you going to come over? You are already 30 minutes late >:(
Josh:(Texts back) give me a sec, I'm on the boss battle.
(Six hours later)
Josh:(texts) I'm ready to come over!