Does the user_enrolments table have a timecreated field?
Yes, it does https://github.com/moodle/moodle/blob/master/lib/db/install.xml#L274
You need to know that in Moodle, dates are stored as an integer unix timestamp. But, if you are using report_customsql, with a weekly scheduled query, that just mean adding
WHERE ue.timecreated BETWEEN %%STARTTIME% AND %%ENDTIME%%
just above the group-by line.
Yes, it does https://github.com/moodle/moodle/blob/master/lib/db/install.xml#L274
You need to know that in Moodle, dates are stored as an integer unix timestamp. But, if you are using report_customsql, with a weekly scheduled query, that just mean adding
WHERE ue.timecreated BETWEEN %%STARTTIME% AND %%ENDTIME%%
just above the group-by line.