Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

The implementation of time serialization in ISO-8601 format is not consistent in the codebase.
In https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/fields.py#L1284 microseconds are included in the serialized value
In https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/utils/encoders.py#L41 only milliseconds are

This is basically the same issue as #4255 except for time instead of datetime.

Expected behavior

I would expect a consistent implementation between the different serialization of time and datetime, i.e. all of them should include microseconds.

Actual behavior

See "Steps to reproduce"