This are some best practices when using APM tools.
There are some instances when you are trying to add a custom date and time, when you want to pick 12:00AM on the Start Time, you have to click a different time first before you will be able to enter the 12:00AM. Same goes to End Time, when you want to pick the 11:45PM, you have to first click a random time before you can enter the 11:45PM.
Page Time Summary
When in Page Time Summary, when you click the the Page Time Details, it will open into a new browser. You won't be able to open another Page Time Details until the breakdown detail on the side of the Page Time Summary stating the Page Time Details you open completely loads.
APM tools supports adding custom date ranges. The dashboard in the APM tool can contain data as old as 60 days. However, if your date range goes beyond the 30 day retention time, this will cause the script details from the Page Time Details to be purged or unavailable.