Oh but thanks to Tinstaafl and Roger_Henshaw for giving me something to work with... !!!
Tinstaafl commented -
"FM is a relatively quick change FROM what existed prior to the stated time to what is expected after that time
BECMG is a relatively slow change over a period of time where the weather starts to change at the beginning of the period, BECOMING the expected weather by the end of the period."
Roger_Henshaw -
"FM plus a time signifies a total change to a TAF (ie all previous info is superceded by the data following the abbreviation FM from the time given.)
BECMG followed by a time period means that some elements of the preceding data are expected to change during the period given, in other words some of the previous data might remain and some of it may change."
Thanks Roger. So in the upcoming CAA UK ATPL MET PRACTICAL exam, I will forego everything that supersedes with a FM! Thats what I am accustomed to anyway learning that in Australia however; do the 30minutes buffer BEFORE apply? As in if the TAF's FM is expected to be TAF FM0204 CAVOK FM0410 +TSRASH, will the +TSRASH effect me in planning should I plan to arrive at 0330?
Also, confirm that FM's are (like above two times) 0400Z to 1000Z and not 04:10Z.
Thanks so much guys. Really, Thanks.
Johan