In what Time Inc. called the first steps of that plan, the company said it will sell 20% of its American Television & Communications unit’s stock to the public. The unit is the nation’s second-largest cable-TV operator. Proceeds of that sale would then be used to help finance future acquisitions that Time hopes will bolster the growth in its magazine and video businesses. Time reportedly has been investigating the possible purchase of Warner Amex Cable Communications, another major cable-TV operator, and Cable News Network. Time said its directors also adopted a “poison pill” provision aimed at discouraging any hostile takeover attempt.