Is It Safe to Use Retin A 0.001% Gel at Night and then Ultraquin (Hydroquinone 4%) During Day Time?

I have Indian skin and have some brown spots on my cheeks. I have tried Mela D with kojic acid for a month and Retin A for 4 months. I put Retin A at night time and Mela D during day time. But since I didnt see any difference so I wanna give my last try to Hydroquinone (4%). But before I do that, I would like to know, if it is safe to use both- I mean Retin A during night and Ultraquin during day time. How long will it take to get any results? Please suggest other procedures too. Thanks!