Hour, Minute, and AM_PM .. and Concatenate this into the Time field

The form you see , lets users select, 

hours from a drop down, 

minute (in 15 min increments) from a drop down

and I have script to a form.. that figures if they mean AM or PM. its only from 9am to 8pm.. so its easy to..

So I would like to have the Time field shown in image... to combine whatever they place in hour, minute, and AM/PM

So that the time field will say [ 10:00 AM ] 

I didn't want to use their system for time, as their are reasons for my madness ::)

Then when they submit the record.. The field Time that has combined ( Hour, Minute, and AM_PM)
So as the go to enter .. this will make Hour, Minute, and AM_PM = in the Time field) and then when they submit .. it has this together.. 

The form name is  new_ws_entry

The bold stuff shows the names of fields. Not sure if its formula that can do this .. or what I should do

So any help in this would be greatly appreciated !