I would like to know how the Populate works in the Timesheet. This seems repeated question , but want to know if there is any updated Document on this for Version 15.2 application.
See if this helps
Submit a Timesheet - CA PPM - 15.3 - CA Technologies Documentation
In addition to Suman's link, please note that the Populate Time Range fields, of the Administration > Project Management > Timesheet Options page, affect which tasks are added to the timesheet. The values are managed by your system administrators, and are set to 7 by default. Using the default values as an example, the date range for tasks that are added during the population of your timesheet is '7 days before the start of the time period' to '7 days after the end of the time period', which is a three week date range.