Exclusively pumping.

Please do not lecture me about “keep trying keep trying” For my own personal reasons, I’m going to exclusively pump. I really don’t want to do formula but will if I need to. Anyway. My milk hasn’t came in yet (baby was born Jan 27th) and I can’t get my breast pump until 5-7 days due to insurance having to mail it to me. I’m not sure what to do knowing my milk is about to come in and all I have is a tiny manual pump the hospital gave me. How long should I pump for to keep a good flow going?