Simply use the Previous() method in your data load script.

Download sample app (.qvf)
https://community.qlik.com/t5/Design/How-to-Calculate-Duration-when-you-have-only-one-date-time/ba-p/2463522#M10088

Do more with Qlik Tips and Tricks Playlist:
https://www.youtube.com/playlist

LinkedIn reference mentioned telemetry app:
https://www.linkedin.com/feed/update/urn🇱🇮activity:7208486658139193346/