I'll be a sec

The phrase used by someone who knows they are gonna come back 2 hours later or not show up at all.

Oscar: Right lads, I'll be a sec. Gonna get a quick snack.

Alan: Ok gdem, he isn't coming back, is he?

Theo: Nah ,probably gonna meet up with Hazel

I'll pop on in a sec

Contrary to popular belief the term actually defines a minimum of 45 minutes passing before anyone will "pop on"

Sam: I'll pop on in a sec.
David: Okay.

45 minutes later
David: Dude?
Sam: Just a sec.