Correct there 'TN' re the pre-flt requirement hence we have 30 hr TAF validity periods for the majors, no operator is gunna be flying the length of a TAF at those major dromes as there's always a new TAF out b4 the current one expires.
TTF's are really only to allow the user/operator to fall within the legal requirements being that they have a 3hr Validity, the Met bureau should put more windows in their buildings that way they might have half a chance to release an accurate forecast:-):-)
Wmk2