How should I interpret this TAF involving TEMPO and BECMG blocks?
TEMPO means that there were be fluctuations in the weather in the time period specified, lasting as long as 50% of the time range specified. TEMPO 0406 0150 FG VV001 means that in the period between 04:00 and 06:00 UTC the visibility will at some point go down to 150 in heavy fog, and it could last up to an hour in total.

One thing I would point out is that the time range for the TAF ends at 06:00, so its very likely the fog will last longer than that.