Для проверки времени суток используйте:
TimeSpan start = new TimeSpan(10, 0, 0); //10 o'clock
TimeSpan end = new TimeSpan(12, 0, 0); //12 o'clock
TimeSpan now = DateTime.Now.TimeOfDay;
if ((now > start) && (now < end))
{
//match found
}
Для абсолютного времени используйте:
DateTime start = new DateTime(2009, 12, 9, 10, 0, 0)); //10 o'clock
DateTime end = new DateTime(2009, 12, 10, 12, 0, 0)); //12 o'clock
DateTime now = DateTime.Now;
if ((now > start) && (now < end))
{
//match found
}