I'm no expert as I've only been pumping for a few weeks, but I have been almost exclusively pumping due to latch + nipple issues. Some days I am not putting her on the breast at all, while others it's 2x per day. I hate pumping, but at least it isn't painful like her latch and, perhaps more importantly, she is getting enough in measurable amounts AND my husband takes over 1-2 feeds every night while I SLEEP. My midwife told me that if I don't pump every 3 hours (which is what is recommended by just about everybody) it isn't a big deal to wait 5-6 hours if I'm using that time to sleep. She said that when you're stressed and sleep deprived and not taking care of your own body then the milk supply starts to decrease. She also recommended massaging the breasts during pumping and using warm compresses/hot water bottle or a hot shower right beforehand. I can tell you that following all of this advice - sleeping more, massaging while pumping, warm compresses (I microwave those bean bag kind while preparing the pump) - has really really noticeably increased my supply and made me feel better. It did take a few days to build it up, but I went from pumping a dismal average of like 20-30 mL (total, from both! I have a double pump too) to averaging 120 mL these days.
My best pump of the day is as the pp said, early morning (like 4am) - I can sometimes pump 180-190mL at that time of the day! I make a point of being up then, so I try to be in bed by 10pm every night and sleep straight through. My husband tends to take over with bottle feeds between those hours so I can sleep.