Bitcoin is upgrading (forking) on or around October 3, 2017, 2:31 pm EDT 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 current block height 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: (hard fork block height - current block height) * 10 * 60