If the [Request Received Date] is actually starting out as date/time then just remove the ToDate function there as that is what is causing it to be converted to a date only and not have any time associated with it. You mentioned the output field type was date/time so I assume this meant your original field there.
You could also use ToTimeOfDay to pull the time out of the date/time field to begin with and work with it from there.
However if [Request Received Date] starts as a date only you cannot pull a time from it.
