Hi again, Jed,
I suspect that Numbers is importing the Excel "Time" as Text. If I am wrong and Numbers accepts a time of day, this method will still work.
Formula in C2 =HOUR(B2)
Formula in D2 =MINUTE(B2)
Formula in E2 =SECOND(B2)
Formula in F2 =TIME(C2,D2,E2)
Formula in F3 = DURATION(,,C3,D3,E3,)
(The extra commas are "Placeholders" for weeks, days and milliseconds that we don't need.)
Confusion may arise from the Cell Data Formats for Duration, h m s
and 0:00:00
That looks like a Time, but it isn't!
Also, please consider tt2's suggestion of decimal time.
Tested in Numbers for Mac version 5.2 under macOS High Sierra. Screen shots may not match what you see in iOS.
Regards,
Ian.