I hate to contradict your doctor but I think one dose before bedtime would be the worst way to dose.  When my son was first diagnosed I did exactly that and he totally stopped growing.  I hope some other people give you their opinions but basically they grow in the middle of the night.  Prednisone can stop growth.  They also need the medication the most early in the morning.  If you give it before bedtime it will probably wear off by the time they need it.

I am dosing my son at 3 AM and upon waking.  I realize this sounds terrible to someone new to this all and it may not be necessary, but it would probably be better to switch to Cortef (a less powerful drug) and dose more frequently.  The most important dose, if you’re not going to do the 3 AM would be right upon waking.