Do this:

TimeFromParts(AppointmentTime/100, AppointmentTime%100, 0, 0, 0)

TimeFromParts() Documentation

Lots of people will use a string-based solution instead, because that's the obvious answer. However, this is a case where the obvious answer is definitely not your best choice. Thanks to cultural/internationalization issues, string-based solutions will pretty much always be slower and more error-prone. If this is how you handled the date conversion, you might also want to revise the Date code to use the equivalent DateFromParts() method:

DateFromParts(AppointmentDate / 10000, AppointmentDate / 100 % 100, AppointmentDate % 100)

If it were me, I'd also combine Date and Time into the same column :

DateTimeFromParts(AppointmentDate / 10000, AppointmentDate / 100 % 100, AppointmentDate % 100, AppointmentTime / 100, AppointmentTime % 100, 0, 0)

I usually do a double cast for int => varchar => date:

SELECT CAST(CAST(20230329 AS VARCHAR(8)) AS DATETIME)

For time, it's something like:

SELECT CAST(STUFF(RIGHT('0' + CAST(830 AS VARCHAR(4)), 4), 3, 0, ':') AS TIME)

You pad out the time to simplify the insert of ':' and then cast to time.

To combine into datetime:

SELECT CAST(CAST(20230329 AS VARCHAR(8)) + ' ' + STUFF(RIGHT('0' + CAST(830 AS VARCHAR(4)), 4), 3, 0, ':') AS DATETIME)