[Date Range] or [Time Range] for duration (e.g. 1 day, 1 week, 14 days, 1 month)
by [Time unit] for x-axis labels (by minute, hour, day, week)
Using the word range implies two points in time, whereas unit implies a divisible (and discrete) point.
If the minimum range is a day, you could use Date Range, otherwise Time Range would allow smaller ranges like an hour.
Some extraneous thoughts on visual hierarchy
One thing I noticed is that the chart labels and title are very close in hierarchy, so I struggle to make out the title. You could try some typographic distinction with a bolder and larger title. I also experimented in shortening the line brackets that divide your units of measure, trying to turn some visual noise created by the deep dividers.
And maybe put title on top, so my eyes first scan the title (especially if it's competing with other page elements or charts) so I can judge what's important, and then start making sense of the data: