Bitcoin is upgrading (forking) on or around November 18, 2017 based on the SegWit2X code on block height 494784. This is a simple count down timer that calculates the targeted fork block height minus the last updated block height (updated every ~2016 blocks) multiplied by the Bitcoin 10 minute block time interval. This is a rough estimate and unfortunately not 100% accurate since not all Bitcoin blocks are found exactly in 10 minute intervals due to the time in between difficulty adjustments as explained here.
Timer Calculation: (494784 - last updated block height) * 10 * 60