If you need to convert a string to a DateTime you could try
DateTime dt = DateTime.Parse("01:00 PM"); // No error checking
or (with error checking)
DateTime dt;
bool res = DateTime.TryParse("01:00 PM", out dt);
Variable dt
contains your datetime, so you can write it
dt.ToString("HH:mm");
Last one works for every DateTime var you have, so if you still have a DateTime, you can write it out in this way.