Both CFL and outdoor grow

Small hobby grow here. How would my plants go if I let them get mostly natural sunlight for 8-10 hrs but then in the afternoon grow them under CFL for 6 or so more hours ? being a cheapskate that I am it's crazy to grow for 18hours under lights when it's beautiful and sunny all the time outside. CFL to be used only 6hrs a day or in crappy weather.

They should end up perfect hopefully

Well, I've only heard of this grow technique recently, but it seems like a good handful of others do this as well.
If you manage to get 10 hours of sunlight, then put it under the CFL's for 8 hours. If it only gets 5, put it under the CFL's for 13 hours.
As long as you have a 18/6, 16/8, or any kind of vegging 24hr light cycle, you should be good.
I wish you the best of luck.