Since Seattle has a week 4 bye and Engram's injury was projected to be a 6-8 week injury when it happened, my educated guess would be that he returns week 5. It's hard for me to be any more optimistic about a quick recovery from a 35y.o. WR.
Branch had surgery for a blown knee in January 2008 IIRC, which means that if he returns this year, it will probably be at a performance level substantially lower than his previous one, which was never elite.
I love Hasselbeck, but between his ailments, his depleted WR corps, and Seattle's investment in the running game, I'm projecting him as a QBBC guy for my teams this year. Still, Hass is skilled, so I'm buying into Courtney Taylor big time this year.