Critics and theater exhibitors have been thwarted in their attempts to get a peek at Tim Burton's highly anticipated "Planet of the Apes" remake, starring Mark Wahlberg, say reports. The $100 million film's last-minute (and down-to-the-wire) production schedule, especially as it applies to special effects, is being blamed. The L.A. Times reports that the theater owners' screening was pushed back to Thursday, two days later than originally scheduled. The film press will be kept at bay until July 20 -- a week before the film is due to open. Bob Harper, vice chairman of 20th Century Fox, told the paper that the movie is three or four days behind, though other sources claim it goes beyond that. Live-action scenes, including an opening rocket crash sequence, have been re-shot, it has been reported. And studio execs have asked composer Danny Elfman to make the score more heroic so they could sell the film as a "sci-fi 'Gladiator.' " "Tim volunteered to give us the movie for the summer," Harper told the Times, "and they pulled off the impossible." He added that the flick's late-summer release wouldn't hinder its blockbuster potential. " 'The Sixth Sense,' one of the biggest-grossing movies of all time, opened then." Meanwhile, "Apes" is due to have its European premiere at the 54th Locarno International Film Festival, in Switzerland, which runs from Aug 2-12, its director, Irene Bignardi, told PEOPLE.com.