First off, most of us do ‘all-nighters’ to get projects finished on-time. Welcome to the club. haha! Four 90 min programs is a lot of work!
Question, are you exporting directly from FCP or exporting as a Reference file and then importing that into Compressor? Exporting as Reference is faster (Not sure why?) 5 Hours for a 90 min show seems a tad long, but maybe not with only 2GB RAM. What compressor does is do the one part first, for example audio then video, that’s why it starts off fast, then slows down.
My suggestion is to Export and go buy some RAM today. Good luck.