Everyone is unique but I find the easiest way and most effective way to take in learning, is to remove all distractions and work at either a really late or really early time. Also don’t set hard limits in acheivments or time to achieve. Alongside these don’t monitor time frequently. Using this I find I get lost in time and just achieve at a perfect pace, it’s not about the amount of content wedged into a small amount of time but rather the quality content achieved or studied in a comfortable and effective time