When to drop a pump?

Al

I’m 7 wpp and pumping 8 times a day. On average I produce 35-40oz a day sometimes more. Currently I am pumping 6am, 9am, 12pm, 3pm, 6pm, 9pm, 12am, 3am and I’m looking to go 4 hours instead of 3 hours at night. Changing my schedule to 6am, 9am, 12pm, 3pm, 6pm, 10pm, 2am

When can I start to work on dropping that 8th pump?

Edit: my baby is sleeping 4+ hour stretches at night