The first schedule of prices filed by a licensee shall be effective immediately upon filing, but an amendatory schedule or amendments to a prior filed schedule is not effective until ten (10) days after the filing date thereof, except that if any licensee has filed a new schedule or amendments to a prior filed schedule to meet lower posted and filed competing prices in a trade area, and the prices thus posted are not lower than the competing prices sought to be met, the new schedule or amendments shall go into effect immediately if the competing prices are already effective, or at the same time as the competing prices become effective.