How long to see an increase due to pumping?

Sept07b2b

So I've added a pumping session at work as a last ditch effort to boost my supply.  I now pump on my commute (7:30), pump at 10:00, pump at 1:00 and pump at 4:00.  Right now, after 3 days, my total output is still the same, it's just spread over 4 pumps instead of 3. 

How long will it take to see an increase in supply due to an added pump session if it's going to happen?  I'm just wondering if at this point in my BF journey I'm tapped out at a certain amount.  I really don't want to keep the 4th pumping session if it's not going to actually increase my output, so I want to know how long I should wait before dropping the extra session.

TIA