There are several types of channels, but probably the type you are referring to is voltage gated ion channels.
The state in which these channels are, open or closed, depends on the action potential across the cell membrane.
If the potential is at the correct energy for the channel to be open it will remain open allowing a steady flow of ions through. Once enough ions have passed so that the potential across the membrane changes to meet the deactivation energy, the channel will close. It then enters a refractory period which requires repolarisation across the cell membrane so that the ion is reset ready to open and let ions through again.
Different ion channels have different activation potentials, deactivation potentials and different refractory periods. This results in different rates of opening and closing.
So based on the above, in answer to your question, no gating is not so fast that it is always open. There are significant periods of time where channels are closed allowing no flow of ions and significant periods of time where they are open allowing continuous flow of ions.