In General Industry settings, as long as the cylinders are “connected for use,” that is, as long as the cylinders have the regulators and hose attached, the cylinders may stay on the dolly. There is no time limit for how long the welding/cutting outfit can stay on the dolly.
This is not the case in Construction, where if gas is not to be drawn for 24 hours, the welding/cutting outfit must be broken down and the cylinders put into storage. OSHA states that this is due to the rougher nature of most construction sites.