+Grumbler: Excellent! (only one thing would make it perfect: ...do you spend on IT?

Thanks.
For some reason I prefer using "it" for something material and "this" for immaterial, e.g. process/action like in this case. Am I wrong?

Yes, quite. The difference between IT and THAT is not about material vs immaterial, it's a question of definiteness, like the difference between the definite and indefinite article. To give you an analogy: when you first speak of a peson or thing, you refer to it with the indefinite article. Then, once it's been established who or what you're talking about, you refer to it with the definite article. I'm sure this is already sufficiently clear to you. The same principal applies to THIS/THAT and IT. Once you have established what you're talking about by referring to something as THAT or BY ITS ACTUAL NAME, then you refer back to it with IT: Can you repeat THAT / YOUR NAME? I didn't quite catch IT. If you used THAT here, it would sound like you were talking about something besides THAT or YOUR NAME. In this post, the use of IT would express that you were still talking about PHOTOSHOPPING.

To complicate things, the word IT is a very weak word - so weak, that it can't be stressed. You could never emphatically ask "What is IIIIT?" When you need to stress the word IT for whatever reason, you substitute it with THAT, because it CAN be stressed. So if in your translation you meant to emphasize the time spent on PHOTOSHOPPING as opposed to other things the person should or could be doing, then you would ask: How many hours do you spend on THIIIS? (with a bit of astonishment), which is how I read your translation. I hope this makes sense. If it doesn't, let me know and I'll be happy to explain it further.

Thanks for the explanation. It'll take me some time to digest it.

My pleasure as always