With the calendar open to the month you want, just tap the day you want for your appointment. You won't see anything happen!
Once you tap the day you want, press the + sign in the lower right corner of the screen --
Once do that, a new box will pop on the screen --
Once you tap on the Starts line, another box will pop on the screen where you can drag the date, hours, minutes or AM/PM wheels up or down as needed --
When you are done with the Starts and Ends time, press Done.