Hi Melvyn.
You have picked an interesting TAF to decode, and what CH says is absolutely correct. To offer something that might perhaps add clarity to your question about the BECMG.
Question: the period of BECMG 2408/2411 is a nice improvement compared with the rest of this TAF, when this time period has elapsed, do I then revert back to the main body of the TAF, or do I use the TEMPO 2406/2418 until 18hrs, although after 18hrs it is starting to get worse again...
Just as an exercise read the TAF without the Tempos (don't misinterpret this as me saying they don't matter or can be ignored).
240457Z 2406/2506 VRB04KT 0200 FG BECMG 2408/2411 08010KT 7000 NSW SCT007
The BECMG indicates an overall change in the baseline forecast until the end of the TAF or next BECMG or FRM,
before taking the TEMPOS into account. In this case, between 0800Z and 1100Z the base forecast wind strength is due to increase, visibility to lift from 200m to 7km, and cloud to lift from fog to scattered at 700 feet.
The time of the BECMG just indicates the times between which that change is due to first occur.
On top of this, overlay your tempos for their stated time periods. So in answer to your question "when this (BECMG) time period has elapsed, do I then revert back to the main body of the TAF?" No, a BECMG doesn't revert back. It indicates an overall change moving forwards (this could be solely a change in wind, viz, cloudbase etc or a combination), BUT in this case there are still TEMPOS (PROB40 TEMPO 2406/2418 & PROB40 TEMPO 2418/2506) that are forecast to happen during the period of the nicer weather, and which cannot be ignored. These are the traps
Cylinder Head alludes to.