In my limited understanding, the box mod will give you more air in the system (as will the full exhaust when you put it on)
More air with the same amount of gas means it may run lean, and that is bad.
Less air with the same gas would be rich, and that would be somewhat better.
If it were me I would not chance it for 1 day. - Just me.
I would take my old exhaust off and get ready for Monday and then would have it up that much faster.
I assume you have a Power Commander and map or equivalent? which you could also install tomorrow.
It may not even run right with the box mod anyway.
Good luck!