Instructions. Determine if your Seth Thomas mantel clock is a 7-day clock or an 8-day clock. On most models it will say right on the face of the clock which type it is.Seven-day clocks must be wound every 7 days, and 8-day clocks must be wound every 8 days.nstructions. Determine if your Seth Thomas mantel clock is a 7-day clock or an 8-day clock. On most models it will say right on the face of the clock which type it is.