To change the date format for the text labels in your gallery, you can use the Text function along with the desired format string in Power Apps.
For your 'Start Time' label, the formula should be:
Text(ThisItem.'Start Time', "[$-en-GB]dd/mm/yyyy")
The [$-en-GB] part is a locale specifier that follows the Great Britain format for the date. You can adjust this to other locales if needed.
For your 'End Time' label, you would use a similar formula:
Text(ThisItem.'End Time', "[$-en-GB]dd/mm/yyyy")
These formulas should display the date as "dd/mm/yyyy" as you wanted.
See if it helps @BS10