pabaigosLaikoLaukelis = 01:00;
pradziosLaikoLaukelis = 20:00;
TimeSpan startTime = Convert.ToDateTime(pradziosLaikoLaukelis).TimeOfDay;
TimeSpan endTime = Convert.ToDateTime(pabaigosLaikoLaukelis).TimeOfDay;
TimeSpan diff = endTime > startTime ? endTime - startTime : endTime - startTime + TimeSpan.FromDays(1);
int minutes = (int)diff.TotalMinutes;