Here is your answer (from a cbs update)--see below. The only thing that makes no sense to me is that Magnum would have had close to a full season under its belt by February-- so for it to return after MacGyver finishes its season in the spring, makes no sense--since MacGyver is starting so late in February. That is the shortest season ever for an existing show that was renewed and doing okay in the ratings. Anyway, well good for Magnum, kind of a bummer for MacGyver (I like both shows).
MACGYVER, a reimagining of the classic series starring Lucas Till in the title role, Tristin Mays, Justin Hires, Meredith Eaton, Levy Tran and Henry Ian Cusick, returns for its fourth season Friday, Feb. 7 (8:00-9:00 PM, ET/PT). The same night, HAWAII FIVE-0 moves to its new time period (9:00-10:00 PM, ET/PT). MAGNUM P.I. will return in the spring after MACGYVER concludes its season run.