I just wanted to know if there were any preservatives I could put in cream cheese icing so it could sit at room temp for a while (for a wedding, so 6-7 hours maybe) Any suggestions are greatly appreciated!

I use a cream cheese and real butter based buttercream icing all the time. The powdered sugar acts as a preservative, however I always deliver my cakes very cold...particularly if they are to be out for a while before cutting. It generally takes a good hour to two hours before coming to room temp. You should be fine. I use the same recipe a bakery used for all their cakes and wedding cakes and there were never any problems.