1pm-5pm is only a 4h layover in my book, and that's not enough for a meaningful trip downtown by 747 bus, which doesn't run too often on Sundays. You'd definitely be spending much more time waiting for and being on a bus than actually being in town.
Of course, taxis would be much faster and more convenient on Sundays at that time, but you're looking at 2x$45 - hardly worth it, no?