What is Jekylls first physical reaction to the potions? How does this reaction change thereafter? How long does it take?

"I stretched out my hands, exulting in the freshness of these sensations; and in the act, I was suddenly aware that I had lost in stature....

And hence, as I think, it came about that Edward Hyde was so much smaller, slighter and younger than Henry Jekyll. Even as good shone upon the countenance of the one, evil was written broadly and plainly on the face of the other. Evil besides (which I must still believe to be the lethal side of man) had left on that body an imprint of deformity and decay. And yet when I looked upon that ugly idol in the glass, I was conscious of no repugnance, rather of a leap of welcome. This, too, was myself. It seemed natural and human. In my eyes it bore a livelier image of the spirit, it seemed more express and single, than the imperfect and divided countenance I had been hitherto accustomed ."

It seems it took a day for the transformation to happen, "The night however, was far gone into the morning."