Comparing

Is it in the last hour

if dtDateTime > System.DateTime.Now.AddHours(-1) Then 
{ 
} 

if dtDateTime.AddHours(1).CompareTo(System.DateTime.Now) < 0  //more than 1 hour ago 
if dtDateTime.AddHours(1).CompareTo(System.DateTime.Now) < 0  //less than 1 hour ago 

Is it in the last 24 hours

if dtDateTime > System.DateTime.Now.AddHours(-24) 
{ 
} 

This will not work if convert a datetime to a string and then convert it back because the millisecond component will be lost

System.DateTime dtDateTime1; 
System.DateTime dtDateTime2; 
if ( System.DateTime.Compare(dtDateTime1, dtDateTime2) = 0 ) 
{ 
  'then they are equal
} 

if ( System.DateTime.Compare(dtDateTime1, dtDateTime2) < 0 ) 
{ 
  'then dtDateTime1 is earlier than dtDateTime2
} 

if ( System.DateTime.Compare(dtDateTime1, dtDateTime2) > 0 ) 
{ 
  'then dtDateTime1 is later than dtDateTime2
} 

Dim oReturnDate1 As DateTime 
Dim oReturnDate2 As DateTime 
If Not DateTime.TryParseExact("20150721 12:06:37", 
                     "yyyyMMdd H:mm:ss", 
                     Globalization.CultureInfo.InvariantCulture, 
                     Globalization.DateTimeStyles.None, 
                     oReturnDate1) Then 
End If 
oReturnDate2 = TimeZoneInfo.ConvertTimeBySystemTimeZoneId("20150721 12:06:37", "Eastern Standard Time")