Yes you use it in a METAR, but it is used differently.
FM, TL, AT are used to specify timings within a TEMPO of a METAR.
In a METAR it is used to indicate temporary changes from a certain time.
In a TAF it is used to indicate permanent change of FORECAST with immediate effect.
Dont spread your own confusion onto the lad Jamie23
The answer is as he was originally given, 9999.