| noop | stats count | fields
| eval num=mvrange(0,40,1) | mvexpand num
| eval _time=relative_time(now(),"-".num."d@d")
| eval day=strftime(_time,"%A - %F")
| timechart span=w count,list(day)
Have your search time range be at least: earliest=-40d@d latest=now otherwise you confuse the embedded bucket command by presenting data that's not in the time range.