Add to dhcpd.conf:

# Write logfile
on commit {
    set clip = binary-to-ascii(10, 8, ".", leased-address);

    set clhw = concat(
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,1,1))),2),":",
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,2,1))),2),":",
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,3,1))),2),":",
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,4,1))),2),":",
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,5,1))),2),":",
        suffix(concat("0",binary-to-ascii(16,8,"", substring(hardware,6,1))),2)
    );

    set ClientHost = pick-first-value(
        host-decl-name,
        option fqdn.hostname,
        option host-name,
        "none"
    );

    execute("/etc/sh_cmd/ip_usage_stat/dhcpd_eventlog.py", clip, clhw, ClientHost);

    unset clip;
    unset clhw;
    unset ClientHost;
}

Each dhcp lease IP write to log file, for example /var/log/dhcpd/172.21.0.10.log contain:

Commit IP: 172.21.0.10, with MAC: 60:22:32:26:84:22, and NAME: pc-01 DATE: 2023-06-20 16:56:55.990941
Commit IP: 172.21.0.10, with MAC: 60:22:32:26:84:22, and NAME: pc-01 DATE: 2023-06-20 17:02:01.570685
Commit IP: 172.21.0.10, with MAC: 60:22:32:26:84:22, and NAME: pc-01 DATE: 2023-06-20 17:06:03.487698
Commit IP: 172.21.0.10, with MAC: 60:22:32:26:84:22, and NAME: pc-01 DATE: 2023-06-20 17:15:26.171225
Commit IP: 172.21.0.10, with MAC: 60:22:32:26:84:22, and NAME: pc-01 DATE: 2023-06-20 17:20:26.847612