I understand that the cosmic acceleration (the acceleration of the expanding Universe) is estimated to have a value of something like $10^{-15} m/sec^2/Mpsec$.
My question is: how much this value changed and will change in time? What was the value of the cosmic acceleration 1 million, 1 billion, 5 billion and 10 billions of years ago? What's the estimated value of the cosmic acceleration 1 million, 1 billion, 5 billion and 10 billions of years from now on?
Is this value constant or it changes in time?