The first thing that you need to do when creating your own Custom Report is to select the different widgets that you would like displayed. As you might already know, you can add the widgets that suit you best by choosing from the different widget categories available and then explore their amazing potential.
In the Campaigns Category, one of the widgets included is named "Best Performing Day and Time". This widget provides you with a chart of your campaigns' best performing day and time, based on their open rate. You can also change the time frame of the graph by switching between Hour or Day buttons. Please note that said widget can be filtered by Date.
1. Select the Best Performing Day and Time widget by clicking on the Add button and then tap on Save. 
Your Custom Report has already been filtered by the timetable set for your entire custom report, therefore this filter will be applied to the widget selected as well.
2. In case you want to change the selected timeframe, tap on the corresponding field at the top of the widget's frame. A calendar appears at the top of your custom report's page, where you can choose the specific dates, by which you need to filter your widget. Note that the date filter used will affect the entire custom report since it will be applied to all widgets that are filtered by date.
Please keep in mind that there are several filters to choose from that can be applied to the corresponding widgets. Furthermore, you can always export the data of each widget in order to have them at your disposal at all times.