NBC will take the “Blossom” plunge in shuffling its sitcom lineup next month, moving the established comedy to Saturdays at 8 p.m. starting March 19.The network is also expected to give an ensemble drama from Spelling TV, “Winnetka Road,” a tryout at 10 p.m. Saturday in place of “Sisters,” which will go on hiatus until April. “Blossom” supplier Disney doesn’t figure to scream too loudly about switching the teen hit, since the show’s current 8:30 p.m. Monday slot will go to “Gaby,” a new sitcom from the studio and Sandollar Prods. starring 11-year-old Gaby Hoffmann (“Sleepless in Seattle”). That series, created by former “Roseanne” exec producer Bruce Helford, premieres March 14. Paramount’s “The Mommies,” which has been struggling in the Saturday lead-off position, will move to 8:30 p.m. following “Blossom.” Moving “Blossom” has been viewed as a possibility for some time as a means of trying to bolster NBC’s Saturday sitcom block or open a new night of comedy. Monday also remains one of the web’s best potential time periods for launching a new series, behind “Fresh Prince of Bel-Air,” with several candidates in development for that assignment. Warner Bros.’ “Getting By,” which moved to the Peacock network from ABC this season, has completed production but remains a contender to return next season, the network said.