xdmp:request-timestamp function returns the system
timestamp that is in effect for current query. This timestamp will
remain unchanged for the duration of the query. If you want to get
the most recent system timestamp external to the current running
context during an update statement (for example, if your query takes
a long time to run, and there are other updates occurring in your
database while your update statement is running), you can use
xdmp:eval to evaluate a separate query statement that
returns the system timestamp at the time the xdmp:eval
query is evaluated.
xdmp.requestTimestamp(); => 1234567