I take it all at once because that is how I was taught to do it. I never heard of splitting it up till about 10 years ago. Tried it, didn’t make alot of difference to me. Yes, I am tired in the evening, like now. I have also tried the florinef and the dexa with the cortef or various combinations, and what works best for me is 20 mg. first thing in the a.m.  Every body is different, and I guess mine is just used to doing this way. I don’t know????????????  Maybe I am weirder than I think!!!!!!!  Hahahahahaha