From the NFHS Basketball Case Book:
5.8.3 SITUATION D: A1 or A2 requests a time-out: (a) while airborne A1 is holding the ball;
(b) while A1’s throw-in is in flight toward A2; or (c) when the ball is on the floor at A1’s disposal for a throw-in. RULING:The request is granted in (a) and (c), but
denied in (b), as there is no player control while the ball is loose between players.
Emphasis mine ... can't get much clearer than that!
And, yeah, 50% -- wow!