Yes, 64 bits is not really comfortable for a long-term timestamp format.
The NTP nanokernel uses a 64.64 integer represention https://papers.freebsd.org/2000/phk-nanokernel/ because 32 bits isn't enough above the binary point because it runs out in 2038, and below the binary point you need 64 bits to accurately represent the nanosecond-scale frequency of the CPU's cycle counter to translate it to wall-clock time.
The NTP nanokernel uses a 64.64 integer represention https://papers.freebsd.org/2000/phk-nanokernel/ because 32 bits isn't enough above the binary point because it runs out in 2038, and below the binary point you need 64 bits to accurately represent the nanosecond-scale frequency of the CPU's cycle counter to translate it to wall-clock time.