Ignore milliseconds when comparing two datetimes

I recommend you use an extension method:

public static DateTime TrimMilliseconds(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, dt.Day, dt.Hour, dt.Minute, dt.Second, 0, dt.Kind);
}

then its just:

if (dtOrig.TrimMilliseconds() == dtNew.TrimMilliseconds())