Paramount’s psychosexual drama “Indecent Proposal” debuted last Wednesday and when the dust settled yesterday the figure of $ 24,543,997 rang up on the register. The three-day weekend score, from 1,694 prints, was $ 18,387,632 for averages of $ 10,855. Anyway you slice it, very, very impressive.Discounting inflation, the film slides into 17th position on the all-time weekend grosses list. It’s just a whisper behind such Paramount stars as “48 HRS.” and “Patriot Games.” It’s also the best-ever April debut and the second-best weekend for any film in that month. It’s also the studio’s first film in 10 months to debut at the top of the chart. And last, but not least, it’s great, considering that April is generally thought to be the worst time to open a picture. The last statement should be read with a grain of salt. Apart from natural and man-made catastrophes, there are no hard and fast rules on when a film will or won’t play. In the past two decades such oft-heard dicta as never open a good picture for the summer; never, never play at Thanksgiving, you won’t make it to Christmas; and January is box office poison have been virtually erased from the showbiz lexicon. Back in 1975, Universal had this bold plan to release a little thriller called “Jaws” with an unheard-of print and advertising push on 400 screens. Today, a comparable launch would raise eyebrows. People would ask, “Doesn’t the studio have confidence in the film?” Some films broke the mold purely by accident. United Artists thought its 1976 quickie “Carrie” could do a couple of weekends in November and move out of the way for its big holiday release, “Network.” It played right on through and was joined by a quickie, cheapie named “Rocky.” Which brings us to January. Who would want to enter the marketplace when the strongest Christmas pix were churning away and collecting cash and awards? Two guys named Eisner and Katzenberg thought they had the better mousetrap when they launched Disney’s very adult Touchstone in January 1986 with “Down and Out in Beverly Hills.” “I said to them, isn’t that a bad playing time,” recalled writer/director Paul Mazursky. “They said it’s the best time. We’re confident in the picture, we’ll support it with advertising and because there are no new films in the marketplace, you have the least competition.” But Paramount’s Barry London applied the only rule that counts: Strong product will lead the box office and a solid commercial come-on is even better in the absence of competition. So “Indecent Proposal” grabs the gold ring and Fox is the weekend’s distant second with “The Sandlot,” the eighth film targeted at the preteen set in the past month. “Sandlot” emerged out of 1,772 dugouts for a weekend total of $ 4, 918,712 and averages of $ 2,776. Pic is an apparent victim of the glut of kids’ films in the marketplace. “Sandlot’s” arrival was also responsible for forestalling another inevitable event — the $ 200 million crowning of Buena Vista’s “Aladdin.” Any day now it will not only surpass that cume, it was also become the first film to gross more than $ 100 million in 1993. Since Jan. 1, the genial animated romp earned $ 99.4 million through Sunday.