How can I make this part wait less time before going back?

The method below you are using:

local part = script.Parent

for i = 0,1,0.01 do wait()
	part.CFrame = part.CFrame:Lerp(CFrame.new(177.5,0.5,4.5),i)
	wait(0.1)
end 
for i = 0,1,0.01 do wait() 
	part.CFrame = part.CFrame:Lerp(CFrame.new(177.5,0.5,21),i) 
	wait(0.1) 
end

Is pretty ugly, you would have to mess around until you get what you want and its a bit blocky... I prefer tween, I even made my own function, here I'll give you a sample:

local function tween(Part,Prop,Val,timing,TweenType)
    local TweenService = game:GetService("TweenService")
    local goal = {}
    goal[Prop] = Val
    if timing then
        local tweenInfo
        if TweenType then
            tweenInfo = TweenInfo.new(timing,Enum.EasingStyle[TweenType])
        else
            tweenInfo = TweenInfo.new(timing)
        end
        tweenn = TweenService:Create(Part, tweenInfo, goal)
    else
           local tweenInfo = TweenInfo.new(5)
        tweenn = TweenService:Create(Part, tweenInfo, goal)
    end
    return tweenn:Play()
end

tween(part,"Position",CFrame.new(177.5,0.5,4.5),1)
wait(1)
tween(part,"Position",CFrame.new(177.5,0.5,21),1)

You can even customize the tween type.. Since it can be used multiple times without yielding, you would need to add a wait to it. Enjoy, if this works click accept.