Your supply is highest overnight, so first thing in the morning (or even after the first feed) you'll get the most quantity.

When I pumped, I always did it after a feed and never in the mid afternoon - that's when your supply is the lowest so I usually couldn't get much out (for the time I spent) when I pumped after lunch.

ETA - I had a double electric pump (in the end) so both sides were being done at once. Had to think about why I didn't know what side I started on