Omitting the seconds has not worked for a long time, if ever.
Omitting the minutes too is just nonsensical for a duration
(it is indistinguishable from just seconds).
Set the recording timestamp in the container.
The syntax for @var{time} is:
@example
-now|([(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH[:MM[:SS[.m...]]])|(HH[MM[SS[.m...]]]))[Z|z])
+now|([(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...])|(HHMMSS[.m...]))[Z|z])
@end example
If the value is "now" it takes the current time.
Time is local time unless 'Z' or 'z' is appended, in which case it is
@item duration, d
Set the video duration of the sourced video. The accepted syntax is:
@example
-[-]HH[:MM[:SS[.m...]]]
+[-]HH:MM:SS[.m...]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.