A Temporal.PlainTime represents a wall-clock time, with a precision in nanoseconds, and without any time zone. "Wall-clock time" refers to the concept of a time as expressed in everyday usage — the time that you read off the clock on the wall. For example, it could be used to represent an event that happens daily at a certain time, no matter what time zone.

Temporal.PlainTime refers to a time with no associated calendar date; if you need to refer to a specific time on a specific day, use Temporal.PlainDateTime. A Temporal.PlainTime can be converted into a Temporal.PlainDateTime by combining it with a Temporal.PlainDate using the toPlainDateTime() method.

See https://tc39.es/proposal-temporal/docs/time.html for more details.