How to make part rotate 90 degrees

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#1 
local PivotPoint = CFrame.new(script.Parent.Position)
local Part = script.Parent
local OpenValue = script.Parent.Parent.Parent:WaitForChild("Open")

OpenValue.Value = false

local AngleRotation = 1

local WorldPartCFrame = PivotPoint * CFrame.Angles(0, math.rad(AngleRotation), 0)
local ObjectPartCFrame = WorldPartCFrame:ToObjectSpace(Part.CFrame)

local function Close()
	WorldPartCFrame = WorldPartCFrame * CFrame.Angles(0, math.rad(1), 0) 
	Part.CFrame = WorldPartCFrame * ObjectPartCFrame 
end

local function Open()
	WorldPartCFrame = WorldPartCFrame * CFrame.Angles(0, math.rad(-AngleRotation), 0) 
	Part.CFrame = WorldPartCFrame * ObjectPartCFrame 
end


local MoveTask
local MoveDebounce = false

local function Move()
	if OpenValue.Value == true then
		
		MoveDebounce = true
		repeat
			Close()
			task.wait()
		until Part.Orientation.Z >= 90
		
		Part.CFrame = CFrame.Angles(0, math.rad(90), 0) 
		MoveDebounce = false
		
	elseif OpenValue.Value == false then
		
		MoveDebounce = true
		repeat
			Open()
			task.wait()
		until Part.Orientation.Z >= -90
		
		Part.CFrame = CFrame.Angles(0, math.rad(-90), 0) 
		MoveDebounce = false
		
	end
end

OpenValue:GetPropertyChangedSignal("Value"):Connect(function()
	if MoveDebounce == true then
		task.cancel(MoveTask)
		MoveTask = task.spawn(Move)
	elseif MoveDebounce == false then
		MoveTask = task.spawn(Move)
	end
end)

When the open Value is changed, the part will rotate. The rotation is perfect fine , HOWEVER, i only want it to rotate for 90 degrees, hyowever, I do not know how to check when the Z axis will = 90, and above.

For those who do not know what i am talking about, i placed this in my script so you can know abit of what im talking about. I know its wrong but it should give sense on what im talking about

until Part.Orientation.Z >= -90