If your extraction time exceeds that suggested, coarsen the grind. Conversely, if it is too short, refine the grind slightly.
It is possible to make a smaller or larger quantity. You simply have to make sure to keep the ratio of 1g of coffee to 16g of water. Keep water in the brewer low by dividing your total amount of water into several small increments.
When pouring the water, keep the flow rate low and avoid touching the edges of the infuser too much.