The resolution of this property depends on the system timer, which depends on the underlying operating system. It tends to be between 0.5 and 15 milliseconds.
An alternative to using xtd::date_time::utc_now is xtd::date_time_offset::utc_now. While the former indicates that a date and time value is Coordinated Universal Time (UTC) by assigning xtd::date_time_kind::utc to its xtd::date_time::kind property, the latter assigns the date and time value the UTC time's offset (equal to xtd::ticks(0)).