Picking up an instrument more often is more important than how long you practice it for.
If you’re having trouble learning something you don’t need more time working on it.
You need practice at the skill of getting yourself to work on it.
In other words, you don’t need practice being in the gym. You need practice going to the gym.
You don’t need practice being on the exercise bike. You need practice getting on the bike.
Most skills don’t suffer from your inability to work on them once you’re in flow.
They suffer from not giving yourself enough practice at getting into a state of flow.
You can watch the video version below.