I personally think it would be best to stick with it once a day, at night as directed. Using it twice a day would just cause much more irritation then needed, and also using it during the day would increase the sensitivity to the sun and such. I just feel like it would be counter productive to use it more then once a day.
Hope this helps!
Wearing during the day can be bad because of increased sun sensitivity. If you can see sunlight, you are being exposed. Even if you are in the shade, or inside with the blinds open.
Also, it can be very drying. Differin does not "stop working". It is active for as long as its on your skin. Additional applications will not improve effectiveness. As long as you haven't washed it away, it's still working and more will just increase the dryness and peeling.
Talk to your doc, maybe they can increase the medication percentage. Also, Differin works by increasing cell turnover and sloughing off of dead cells. Your skin cannot grow any faster than it already is. You risk having a raw, red face that is more prone to scarring due to sun sensitivity.
People who report increased improvement with multiple applications are probably washing thier face in the Am, applying and then applying after washing again in the evening. I have pretty hardy skin, and can't imagine peeling any more than I already am.
I have been applying differin morning and night for 12 weeks. My dermatologist said to start off applying just at night and if my skin had no/minor irritation from applying once per day to start applying twice. Being in the UK I don't have to worry about being out in the sun!!!