Find if current time falls in a time range

Some good answers here but none cover the case of your start time being in a different day than your end time. If you need to straddle the day boundary, then something like this may help:

TimeSpan start = TimeSpan.Parse("22:00"); // 10 PM
TimeSpan end = TimeSpan.Parse("02:00");   // 2 AM
TimeSpan now = DateTime.Now.TimeOfDay;

if (start <= end)
{
    // start and stop times are in the same day
    if (now >= start && now <= end)
    {
        // current time is between start and stop
    }
}
else
{
    // start and stop times are in different days
    if (now >= start || now <= end)
    {
       // current time is between start and stop
    }
}

Note that in this example the time boundaries are inclusive and that this still assumes less than a 24-hour difference between start and stop.

A simple little extension function for this:

public static bool IsBetween(this DateTime now, TimeSpan start, TimeSpan end)
{
    var time = now.TimeOfDay;
    // Scenario 1: If the start time and the end time are in the same day.
    if (start <= end)
        return time >= start && time <= end;
    // Scenario 2: The start time and end time is on different days.
    return time >= start || time <= end;
}

For checking for a time of day use:

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
}

For absolute times use:

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
}