I had been reading on LingQ for about 3 hours a day, 6+ days a week since last November. In the past month I’ve been shifting my balance of reading just on my tablet outside LingQ or reading physical books so that number may drop, but I’ll keep reporting words read.
It was challenging for the first 3 months and then it started to get a lot easier, and my progress is pretty astonishing.
That said, I’d probably not recommend JUST using LingQ for 6 hours a day. If you have that 6 hours you can dedicate to input and study, I’d probably cap at 3 hours a day with content on LingQ, and spend the rest of that time with TV, Films, Audiobooks, italki Conversations, Anki/SRS, Writing or just whatever you enjoy doing!
I personally just try more and more to enjoy whatever it is I’m doing and that alone seems to make a big difference. E.g. today I will be going to “allsång” and singing “snapsvisor” and expect it to be a blast :).