How a rolling reserve works, day by day
Suppose your agreement sets a 10 per cent rolling reserve held for 180 days. On a day you process 10,000 in card sales, the acquirer settles 9,000 (less its fees) to your bank account and holds 1,000. That 1,000 sits in reserve until day 181, when it is released to you. The next day's held amount is released the day after that, and so on. Because each day's slice has its own release date, the reserve 'rolls': after the first holding period ends, money is being released every day at roughly the same rate it is being withheld.
The important consequence is the ramp-up. During the first holding period nothing comes back, so the reserve balance grows until it equals roughly the percentage multiplied by the sales of the whole holding window. With steady volume of 300,000 a month on the terms above, the reserve would level off at around 180,000. After that point your settlement roughly matches your net sales again, but that balance stays tied up for as long as the reserve applies.