Re: zero (0) cycle paths
Multicycle paths are those paths which use more then one clock cycle . Usually DC/PT check path timing in one cycle.
If you have a path in your design ,which cannot finished operation in one cycle, you can tell DC/PT this path is a multi cycle path.
Hold multicycle constraints are based on the default hold position (the default value is 0). An end hold multicycle constraint of 1 effectively subtracts one destination clock period from the default hold latch edge