In a distributed system there are as many clocks as there are systems. The clocks are coordinated to keep them somewhat consistent but no one clock has the exact time. Even if the clocks were some what in sync, the individual clocks on each component may run at a different rate or granularity leading to them being out of sync only after one local clock cycle.
Time is only known within a given precision. At frequent intervals, a clock may synchronize with a more trusted clock. However, the clocks are not precisely the same because of time lapses due to transmission and execution.
Consider a group of people going to a meeting. Each person has a watch. Each watch has a similar, but different time. Even with the error in time, the group is able to meet and conduct business. This is how distributed time works.
This is in contrast to a clock on a single system. Here there is only one clock and it provides a unified time for all sub components on this individual system.