Hi
your time values in col B are text looking like time, not real times.
To solve, in an unused column, insert =timevalue(B5) and drag down to the end of the range.
Copy then Paste Special Values over col B - Format as needed

Then rebuild your graph

__________________
Using O365 v2503 - Did you know you can thank someone who helped you? Click on the tiny scale in the right upper hand corner of your helper's post