Is there a Formula to Predict Delta Temperature based on previous trend?
You've already been given good answers, so I won't expand on those. I just point out something no one seems to have mentioned: extrapolation of a function value can be risky if you don't have some theoretical justification that guarantees that the extrapolated curve follows the model you have chosen. In other words you must be sure in advance that the "shape" of the actual curve (noise aside) matches that of the model, otherwise you should check that the results make sense. From what you say it seems that your systems all follow the same pattern (some sort of thermal "RC" equivalent circuit with a exponentially flattening response, like the charge of a capacitor), so you should be safe. If you deal with systems/test setups which exhibit a different pattern be aware that you will have to change your model.