Trying to get the difference between two date/times

[Masterkirkby]

So I've created two difference date objects

I save them to my shared preferences and recall them later to find the difference in the two. However, since these are saved as strings, and converting them to integers doesnt work because of the format, how can I go about finding the difference?

 

[Unforgiven]

A long time ago when I was writing code a datediff function was hit or miss depending on the language. I found this for Java which looks like some of the workarounds I had to do in other languages, more or less do some data conversions and some math.
https://www.baeldung.com/java-date-difference

 

[Masterkirkby]

I found a method, I made hour/min/sec into an int and passed them through sharePref. Then I did the math and concatenated them.