Palmer tore his ACL and MCL as well as having cartilage and meniscus damage and dislocation of the patella. A pretty devastating, career-threatening injury that also happened in the act of throwing which IMO, could have added to the time it took for him to "get back on the horse" so to speak.
Brady tore the ACL and MCL and after surgery had infections.
Bradford tore the ACL only. RGIII had a similar injury and returned in 8 months. Palmer's and Brady's injuries seem much more severe.
Bradford had successful surgery on 11/19/13 so that gives about 9 months before training camp. Will probably miss some OTA's but as long as he gets a relatively full training camp, things should be fine.