My friend just told me lunch in a bit, I think that means have lunch for little bit, and I googled the meaning of "lunch in" and "in a bit", but couldn't find the answer, anyone could answer this question? Thanks so much!
In a bit is a vague time expression that means "sometime later."
X in a bit doesn't refer to the duration of X, but the fact that X will happen at a later time.
You can say "X for a bit" to refer to the duration of X similarly.
I'll be available in a bit. (I will be available sometime later, not an exact or determinate time)
I am available for a bit. (I am currently available for a short amount of time, not an exact or determinate amount of time)
I'll be available for a bit. (At some point in the future, I will be available for a short, indeterminate amount of time.)
This is similar to "in a while/for a while".
The phrase "lunch in a bit" is typically an invitation to lunch, the meal typically eaten at midday, in a short time (time denoted with the word "bit"). With the question mark omitted I can understand your confusion.