Or there is another issue, the raid would be tuned expecting players to have the set pieces (at least 2pc if not 4pc) to continue progression. Which could mean that without the set pieces players would need to perform at a higher level. Granted this isn't as big of an issue for top end of raiders but it would be very punishing for rest.
Besides, are we forgetting that there are other sources to get gear? We'll still have M+ and some form of the Great Vault. The crafting systems in DF seem to allow normal/heroic raid level gear to be crafted (provided you farm the mats).
6 Weeks is fine IMO.