I don't recall exactly how long I studied for math everyday, but it was very long. At its most intense, math preparation included review of the
Manhattan books, practice and review Jeff Sackmann's math sets or OG (as many questions as possible), and practice and review one GMATClub test per day. Eventually, my routine included one GMATClub test and some light math reading. I would start with math and then switch to verbal when I became exhausted. And once verbal wore me out, I would switch back to math. This allowed me to go past the breaking point. I gradually built up to studying almost the whole day. Breaks included meals, gym time, and some light web surfing. But even then, most of the latter was on GMATClub. I even read (or re-read) GMAT books while in the bathroom!
Fortunately, most don't need to take such drastic measures for results. But I was desperate and knew that I had to push myself to the max to reach my potential. This is not always possible (nor advisable) for most test takers due to family obligations, work, and school. But it's important to push yourself and improve. If you make things too easy, then there's no resistance and no growth.