Phil
If you get the flow control, you will need two valves. If you get a needle valve, you will only need one per cylinder.
I found another unit called a snubber or restrictor that goes in line , no cutting, and you would only need one of these per cylinder. They have different orfice sizes to match your requirements.
You would only unhook the line from the cylinder and put the restrictor on, be sure to match up fittings type.