It's not always the length of time, but the techniques you use. Focus helps too, as others have mentioned, eg scales, arpeggios, etc, focus on the very basis of what tunes are made of.

When learning medieval sword and shield, I did a couple of tricks. One was to close my eyes and feel what was happening, and visualize internally 'the picture of the little dancing puppet man in my head' doing it. Just tell the little man in your head to do, and it happens - faster than actually reacting to what is happening in front of you, and thinking about it.

Another trick is to 'swap hands'. I used this many years before when doing foil. I also found it helpful when first learning whistle. Putting the other hand in charge means that you use other parts of the brain. Swapping back to the first handedness again means that yet other parts of the brain start to work in a 'meta state' as the brain realizes that it has more than one source of learning the skill. The skill level soon jumps quite a bit, giving a more rapid skill increase to the beginner.

I also swapped hands for a while when first learning the piano accordion, but because of the construction of the instrument, this can only work easily for the smaller boxes. The way the straps are affixed, Chin Masters, etc are fixed, and some things are thus not reachable ... :-) And some instruments are just not physically amenable to this trick....