I usually take my entire daily dose first thing in the morning. Since it has a half-life of 1.5 days, there really is no need to worry about your levels fading that much between doses. Plus, if you split your dose up and take half of it later in the day, you might have trouble sleeping.
Exceptions to my dosing guidlines: if I am doing cardio first thing in the morning, I wait till after the cardio to take my dose so that my heartrate doesn't get alarmingly high. Also, on the days that I do legs, I wait until after my workout to dose my clen. You will have a horrible lift and feel weak and sick if you have clen going through your system when you do legs. If my leg workout isn't until late in the day, I just skip my dose for that day.