This clock is showing the Bitcoin Time from the bitcoin network. Bitcoin nodes communicate with each other and exchange timestamps. To avoid reliance on any single clock, each node keeps track of the times reported by its peers. Bitcoin then uses the median time past (MTP) mechanism. In this fantastic time piece provided by the Banglafresh Foundation, the timestamp is an average of the latest 5 blocks of the bitcoin network currently using blockstream.info API. Feel free to copy and use Bitcoin as your go to clock and not only as currency.