Templates use views, and you can modify the timesettings of a view. But a bit more info is needed here, what kind of report are you trying to create? What should it contain as in objects (virtual machines, hosts, cluster..)
Lets take the capacity report as an example here;
Look up the report and edit it:
Search for the view name as show in the right pane and edit the view
In the edit view go to Time settings and adjust as required.