My 7 yr. old SW CAH boy just had an increase in Cortef due to high 17OHP, over 4,000, and some clinical manifestations of undersurpression, still a bone age that lags about a year, anyway, he said he felt better right away with the increase in cortef. He said I can play football at recess instead of just walking around, he had never complained of low energy or being tierd, but I think with the increase in meds he has a real increase in energy, I would say within 3-4 weeks his physical signs of undersurpression had gone away. I hope this helps.
The endo about a year ago decreased his meds to try and get him to grow a bit, he grew 6 inches this year. Wow! Otherwise his meds have been very stable.