The box Date/Time range on the left has ready-made choices:
To choose your own dates, click on the button that shows the two dates (or on the From or To line in the heading of the report). A small window opens where you pick the day on a calendar and the time, for the start and for the end. Move the mouse out of the window to close it.
Moving the From date past the To date takes To along, keeping the length of the period (and the other way round), so another day is one click: choose the new From date and the report shows that day.
When there is nothing in the chosen period, the report says so and tells you when the latest clocking and the latest download were; click Show that day to see it. A report about one site also says when the period has clockings at other sites.
Baton, By Download and Groups/Points have no dates: Baton and Groups/Points cover everything ever downloaded, By Download shows one download.
After a download the report moves to it by itself, see Downloading a baton.
The Site box only shows when there is more than one site. Choose the site in the box, or click on the Site line in the heading of the report (left click for the next site, right click for the one before it).
Detailed, Overview and Site statistics are about the chosen site. Baton and Groups/Points show the chosen site too, or every site when you choose All sites at the top of the box. Downloads and By Download do not depend on the site.