Hi @RoyWaarts_NL ,
Do you want to only display time value regardless of date value in powerapps?
Did you set your time field in Excel like this?

If so, I've made a similar test and found that:
if you directly use "ThisItem.start" in your gallery, it will show data like this:
12/30/1899+time value.
"12/30/1899" is the default date value of Excel in powerapps.
I suggest you use Text function to format the data.
You could set the label's Text like this:
Text(ThisItem.start,ShortTime)
//Text(ThisItem.fieldname,ShortTime)
Text(ThisItem.end,ShortTime)
Then the label will only display time value.

Here's a doc about Text function for your reference:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-text
Best regards,