reduce pumps

I'm going back to work soon and unfortunately my job does not allow me to pump so frequently and on time. I used to pump 2 hourly and has gradually pulled the duration longer. now pumping 4 hourly yielding about 1.1L in total/day. I can't seem to find answers on google so I'm asking for help here. anybody with similar situation? I plan to drag out to pump 6 hourly instead but wish to keep supply at least 1L/day. how do I adjust? increase duration from 4 to 5 hourly then 6 hourly gradually? I'm worried supply will drop as my body thought I don't need so much milk. TIA.