Programming is hard

tests.cs

[TestMethod]
public void Can_Handle_InTimeSpan()
{
    var testtime = DateTime.Now;
    var start = testtime.AddHours(-3);
    var end = testtime.AddHours(3);
    Assert.IsTrue(testtime.InTimeSpan(start, end));
}
        
[TestMethod]
public void Can_Handle_InTimeSpan_24h()
{
    var testtime = DateTime.Now;
    var start = Convert.ToDateTime("1900-01-01 07:00");
    var end = Convert.ToDateTime("1900-01-01 07:00");
    Assert.IsTrue(testtime.InTimeSpan(start, end));
}

wtf.cs

/// <summary>
/// Check if a time is in the span
/// Only checks TimeOfDay
/// </summary>
/// <param name="time">The time to check</param>
/// <param name="startTime">Start time</param>
/// <param name="endTime">End time</param>
/// <returns>True/False</returns>
public static bool InTimeSpan(this DateTime time, DateTime startTime, DateTime endTime)
{
    TimeSpan start = TimeSpan.Parse(startTime.ToString("HH:mm")); // 10 PM
    TimeSpan end = TimeSpan.Parse(endTime.ToString("HH:mm"));   // 2 AM
    TimeSpan now = time.TimeOfDay;

    if (start < end)
    {
        // start and stop times are in the same day
        if (now >= start && now <= end)
        {
            return true;
        }
    }
    else if (start > end)
    {
        // start and stop times are in different days
        if (now >= start || now <= end)
        {
            return true;
        }
    }
    else
    {
        return true;
    }
    return false;
}