You can make ranges by months to show it in a drilldown since the days of the months are varied
Use relative-time specifiers like @mon
for the start of this month and @mon+1mon-1day
for the end of this month, e.g.:
|makeresults
| eval start=relative_time(now(), "@mon"), end=relative_time(now(), "@mon+1mon-1d")
| convert ctime(*)