i still get tired in the afternoon. by about 4 i've already been up for almost 12 hrs so sometimes i will take a 10min power nap if i can. can't do that everyday so i just push through it. usually if i'm super busy i don't think about being tired. i have tried exercising in the afternoon, like between the hours of 3 to 6, but for me its like pulling teeth. i have to stop everything that i'm doing to workout. i'm still tired at that time too so i literally drag during my workout. 5am is the best for me. when i don't workout in the morning i feel groggy all day. my favorite time to workout is at 9 or 10 am but my schedule doesn't allow me to do that.