It sort of depends on what else happens in the multiverse while the wizard is stuck in his tower muttering over esoteric carvings.
If the fighter's wife gets kidnapped two weeks into the creation, is he going to say "Well, the wizard needs another 5½ months to finish his fine dohickey staff. I'm sure Sarah wouldn't mind waiting around...." Probably not.
Life: Its what happens while you were making other plans.
Exactly my point.
While it may only take a few seconds of real time to cover 6 months of game time - what are the PCs that are not crafting items do during that time?
Spending money?
Getting into trouble?
Plying their own professions? (This of course almost forces all PCs to take profession skills just to have something to do during the down time).
If you use the optional training rules then that time could be used for that - but then the crafter has lost out on precious training time himself.
When things are reduced to mere sentences then a lot of the PRGing is lost and we end up with combat oriented games where everyone "resets" between combats. {Hmmm I think there is a game design that follows that pattern already. . . . }