Steps to make sure you can use AM and PM in Datacards PowerApps

1. Insert Drop Down to Date Data Card, within the card. 

2. Add this to the drop down "Items" property.

["AM","PM"]

3. Add this formula to the DataCard's "Update" property. (Change the formula to your data card information)

DateValue8.SelectedDate + 
Time(
   If(
      Dropdown4.Selected.Value = "PM", 
      12, 
      0
   ) + 
   Mod(
      Value(
         HourValue8.Selected.Value
      ), 
      12
   ), 
   Value(
      MinuteValue8.Selected.Value
   ),
   0
)

4. On the Hour control of your data card put the following:

a. in the "Items" property:

["12","01","02","03","04","05","06","07","08","09","10","11"]

b. in the "Default" property:

Text(If(Mod(Hour(Parent.Default), 12) = 0, 12, Mod(Hour(Parent.Default), 12)),"00")

That should do it. :)