First get the text from the textbox and try to parse it into a DateTime format.
Then get the time of day as a string.
string date = string.Empty;
if (!string.IsNullOrWhiteSpace(textBox1.Text)) {
DateTime timeDate = new DateTime();
if (DateTime.TryParse(textBox1.Text, out timeDate)) {
date = timeDate.TimeOfDay.ToString();
}
}
if (!string.IsNullOrWhiteSpace(date)) {
}