You can take them all at once as Clen is in your system for 36+ hours. But as with anything your body would appriciate breaking the dose up throughout the day, don't take them late though as it will keep you up. That schedule looks fine, you can go higher than 80 though, up to 120 is fine. Feel it out once you start taking you will know what your limits are. The sides are nasty though be prepared...Taurine and Potassium will help, you can buy Taurine in a powder form and Potassium in pills...
I stopped though because the sides were too much for me.