Option Explicit

Sub tst()

Dim dtmNormal    As Date
Dim dtmUTC       As Date
Dim ss  As Long
Dim hh  As Long
Dim mm  As Long

dtmNormal = Now
dtmUTC = Now -  0 . 123  'число взял произвольное

Debug.Print dtmNormal
Debug.Print dtmUTC

ss = Abs(DateDiff("s", dtmNormal, dtmUTC))
hh = Fix(ss / ( 60  *  60 )) *  60  *  60 
mm = Fix((ss - hh) /  60 ) *  60 

Debug.Print Fix(ss / ( 60  *  60 )) & ":" & _
            Fix((ss - hh) /  60 ) & ":" & _
            ss - hh - mm & " hh:mm:ss"

End Sub

dtmUTC = DateAdd("h", +-нужно число часов, dtmNormal)

If a >= CDate("30.03.2008 02:00") And a <= CDate("26.10.2008 03:00") Then
    Debug.Print "Летнее!"
Else
    Debug.Print "Зимнее!"
End If