It's a implementation of "TCP Based Time Service" Time Protocol [RFC868].
./timed-rs # default port usage (0.0.0.0:37)
./timed-rs 0.0.0.0:3737 # specific port usage
NOTE: 37 is a well-known port. It may require administrative permission.
$ nc 127.0.0.1 37 | xxd
00000000: e8f7 1e9a ....
$ rdate 127.0.0.1
rdate: [127.0.0.1] Thu Nov 9 18:02:18 2023
4