Force Tween Service to go a certain direction?

I have a setTime function

local function setTime(result,speed)
    local TimeSetInfo = TweenInfo.new(speed)
    local goal = {ClockTime = result}
    local Tween = TweenService:Create(Lighting,TimeSetInfo,goal)
    Tween:Play()
    wait(speed)
end

I want the night and day to be different lengths when I set the time to 17.67 at a certain speed then go to 6 it goes backwards is there any way to force the time to go forward