When my son was born (nearly 16 years ago) most patients with CAH were only given hydrocortisone twice a day, so 7am and 7pm was his dosing schedule.  It changed when he got to 7 years old as he did start to tire after school and new papers stated that thrice daily was a better regimen.  Since then doses have been given at 7am, 4pm (after school) and 9pm.  He does well on this schedule and 24 hour blood profiles prove his CAH is under good control.  If your daughters are well and blood tests show their present medication regimen is controlling their CAH, then I wouldn’t worry - why fix what isn’t broke (as they say)?