Timeout period should be 48 hours for a notification.
1. Go to particular Notification Label
2. Select the properties
3. Select the Node tab
4. Change the Timeout type to Relative Time and enter the value as 2 days or 48 hours.
Consider AP Invoice Approval Workflow
Open workflow from database in workflow builder
File -> open -> select radio button for database
Select the Invoice Workflow (AP Invoice Approval).
Open process and select the notification to change the timeout period.
Change the value to 2 days.