Hi Kamal,
UI extension points are delivered in the standard.
App Extensibility: My Inbox - SAP Fiori for Request Approvals 1.0 - SAP Library
Customers have their freedom of choice from different options.
+ You can use Approve Timesheet App
+ You can use My Inbox with open task function
+ You can use My Inbox with SWFVISU customizing
+ You can use My Inbox with html content generated by BADI
+ You can use My Inbox with extensibility
+ You can build custom app
+ Legacy UI are also available. SAPGUI, WebDynpro...
Regards,
Masa / SAP Technology RIG