Not all people are equivalent. Not all time is equal. Different parts of the learning process will be different.
When you “spend time” on something, how much of that time is truly focused? How long does it take you to switch gears and be “in the zone”? How easily distracted are you? How frequently can you dedicate time?
Different parts of your learning process will place different demands on you. In the early phases, you’ll probably do well with frequent and smallish sessions. When you’re mostly learning new vocabulary and concepts, you don’t want to overwhelm yourself. When you’re working on solving tough problems or building a project, you will probably need both more time and more focus.
Basically, it’s very much the same as your language studies or guitar. Consistency is key, but if you only ever dabble for half an hour at a time it will be hard to acheive significant skill increases.