Sure= yes/okay -informal
In a bit= in a 'bit' of time where bit is a few second up to a few minutes and implies when you are free to do this and that it doesn't need to be done this second
(bit has nothing to do with computers)
-something you would say to a friend informally...not to your boss, not to a client
Sure, in a bit=okay, I will do that soon/in a few moments/in a little while/l will get to that soon
Generally, not a sarcastic thing to say, but if a parent said to their teenager, clean your room(because it is a disaster) and the child says, sure, in a bit....there will be trouble!
Hope this helps
I sure hope that you can use this sentence in a bit