code:

---

Function GMT_Time($Time)
	; Returns GMT time from local time
	; Also return Global var: $GMTDay (-1 = Yesterday, 0 = Today, 1 = Tomorrow) 
	Dim $Min,$Sec,$Bias,$Tmp,$H,$M
	Global $GMTDay
	$GMTDay = 0
	$Min = Val(Left($Time, 2)) * 60 + Val(SubStr($Time, 4, 2))
	$Sec = Right($Time, 3)
	$Tmp = ReadValue("HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation","ActiveTimeBias")
	If ReadType("HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation","ActiveTimeBias") = "REG_BINARY"
		For $i = Len($Tmp) - 1 To 1 Step - 2 ; Reverse binary string to Hex string (Win 9x)
			$Bias = "" + $Bias + SubStr($Tmp, $i, 2)
		Next
		$Bias = Val("&" + $Bias)
	Else
		$Bias = Val($Tmp)
	EndIf
	If $Bias = 0
		$GMT_Time = $Time
		Return
	EndIf
	$GMT_Chg = $Min + $Bias
	Select
		Case $GMT_Chg >= 60 * 24
			$GMT_Chg = $GMT_Chg - 60 * 24
			$GMTDay = 1 ; Tomorrow in G
		Case $GMT_Chg <= 0
			$GMT_Chg = $GMT_Chg + 60 * 24
			$GMTDay = -1 ; Yesterday in G
	EndSelect
	$H = $GMT_Chg / 60
	$M = "" + ($GMT_Chg - $H * 60)
	If Len($M) = 1
		$M = "0" + $M
	EndIf
	$H = "" + $H
	If Len($H) = 1
		$H = "0" + $H
	EndIf
	$GMT_Time = $H + ":" + $M + $Sec
EndFunction

---

For GMT Date/time look in: GMT_DateTime - Transform local time to GMT (date and) time

-Erik