In my limited experience, the existence of a sheath on a catt tells you little about how soon it will flower. I've had some that bloomed out of green sheaths. I've had some that bloomed out of dried sheaths that were that way for months. I've got some now which have had sheaths for almost a year, but I know that I've caused them enough stress that they probably won't bloom until the next season/mature growth. Recently, with the hot & humid weather we've been having, I have two that have pushed up buds on new growths that have no sheath at all!
Proper culture and the proper season are better predictors of when a catt will bloom. It's not always easy to figure out the season on hybrids. Some bloom on every newly mature growth, others hold their sheaths and wait til the proper season. Maybe yours is a fall bloomer? Keep the plant happy and be patient.