I know this is not supported on older products. But KNOT is a new product, so perhaps the designers have finally added that one extra PCB trace to connect the 1PPS signal from the GPS module to some CPU interrupt pin? I have successfully built a Linux NTP server where the PPS goes to the software defined pin (SDP0) of the i210AT NIC which does hardware timestamping, it works very well but still needs a power-hungry x86 box. Could the KNOT do the same with much less power?
Even if they did neither the chipset or RouterOS has that kind of timing support.
Are you sure about the chipset? While it may not support nanosecond timestamping of Ethernet frames for PTP (as some good Intel NICs do), most such chips do have a high-resolution timer which can be read in the interrupt handler (from GPIO or serial port control line). Still much better timing accuracy (microseconds) than cheap USB GPS devices (USB is the problem here, adds about a millisecond of latency and jitter, and few devices bother to connect PPS to one of the serial port control lines - it is much worse if they don’t).