No, DateTime uses 24-hour time, so parsing "5:00" will always return the equivalent of 5 AM.
"Work hours" are not constant, even within a culture (maybe I work at night!) so any kind of logic like this needs to be written by you, and is not provided in the framework.
This logic could easily look like:
if (time.Hour < 9) // less than 9AM, it must be PM!
time.AddHours(12);