I also pump at work. I do not have a "pumping" room which I have to reserve- that would be nice!. (I pump in the electrical/plumbing room!). I find that if I miss pumping sessions, my supply drops. They say that one should pump 2-5 minutes AFTER the milk stops just to keep stimulated enough to keep up with supply! I would be a bit nervous to only have one "good" pump a day. -but it is good that you at least pump for that 5 minutes...that is crucial in fact. How long have you been pumping at work? My supply was great for the first month I was back at work....I could skip pump sessions or shorten others and my supply would stay the same....but not anymore! I really have to stay on top of it. At least with my job, I'm not confined to a time restraint (I just have to fit it in between clients and meetings, which is a challenge). I wish you the best, because I so know how difficult it is!
I would also look into "booking" another slot around 4:00 or so- at least to pump again on one side. (I like to keep one side "full" for when I get to feed my lo for bedtime)