@classmethod<EOL><INDENT>def at_time(cls, at, target):<DEDENT>
at = cls._from_timestamp(at)<EOL>cmd = cls.from_datetime(at)<EOL>cmd.delay = at - now()<EOL>cmd.target = target<EOL>return cmd<EOL>
Construct a DelayedCommand to come due at `at`, where `at` may be
a datetime or timestamp.