DateTime.Ticks will account for the time. Use .Ticks on the DateTime to convert your dates into longs. Then just use a simple if stmt to see if your target date falls between.
// Assuming you know d2 > d1
if (targetDt.Ticks > d1.Ticks && targetDt.Ticks < d2.Ticks)
{
// targetDt is in between d1 and d2
}