I just assumed from what I had read that we can shift them by for example working nights or going to bed later at night on a regular basis.  I read this on the written information which was printed on with the graph that the Mayo Clinic did with their studies.  I reckoned it must be true to a certain extent as otherwise we would not be able to work nights or do all that stuff and that our bodies would be all messed up.  As some folks work nights for years---I assumed that they do manage to shift their rythyms.  I can identify with this also because when we emigrated from the UK to New Zealand, the time was some 12-13 hours ahead of the UK.  For a long time I would wake at 3.00am in the morning and feel hungry at all the wrong times for the wrong stuff.  It took a while to get my body in sinc with the time here.  I'd say that that stuffed with my cortisol levels when I reflect back too as I was feeling pretty tired during the day and wanting to sleep in the afternoon NZ time. 

I basically based my assumptions on all of the above and what I have read from that article.  Maybe we should look further into this.  I think with children though, they usually get put to bed quite regularly atd they arn't kept up late so generally you can relay on their body rythms where dosing at the right time is concerned.  If Ashley is over excitable as he was Christmas eve and has not gone to sleep (he was still awake at 1am in the morning) I have given him his hydrocortisone and not waited until 2am because I knew that he was pretty alert and had not had a dose since 3.15pm.  I figured that he certainly was not having the low cortisl levels that he should at midnight in deep sleep so I was concerned and gave his 2am dose right away.  Hope that this all helps you with your childs growth Adina. :)