When are these supposed to be changed out? I usually get 4-5 oz at 10 am, 2-2.5 at 12, then 3-3.5 at 2 pm when I pump at work with an old PIS (waiting to get a new PISA from insurance). I've been using the current set for the past 3 months and this has been the pattern this whole time so not sure I need to change them since they lay flat. I use my freestyle at home when I pump in the morning. Turns out having to wash all those freestyle parts at work was more cumbersome than washing the PIS parts (mainly drying was difficult) and my friend gave me her old pump so I figured I'd just keep that one at work.