DHCP Options for Network Time Server

From a Google search, first result:

Option 004 specifies servers that provide TIME/ITP (as per RFC 868). This is not a recommended protocol/service in a Windows environment.

Option 042 specifies servers that provide NTP/SNTP (RFC 1769). This is the preferred time service in a Windows environment (assuming the absence of Active Directory which maintains the time on your behalf).

• Option 042 refers to NTP (RFC 1769)
• Option 004 refers to TIME/ITP (RFC 868)

Source

The RFC 868 "time" service as specified by Option 4 is pretty much obsolete and only has 1s resolution.

Modern networks should always use NTP (Option 42).