SpringBoot JPA Methods or query to perform arithmetic operations with Postgres columns

[Rocky Droid]

I am a beginner with SpringBoot and accessing postgres table with multiple columns along with two timestamp with timezone columns(start time and end time). Besides retrieving all columns I also want to display time taken in seconds(end time - start time). I am extending PagingAndSortingRepository (findAll) for retrieving with paging and sorting. Please suggest the required solution. Will be using ReactJS for presentation.