I have been chasing this as well. I have a couple songs I want to play that have chords too spread out for me to reach. Our goals may be different, but the idea is related.
When I began guitar, my fingers really pointed to my palm, especially bending the largest knuckle. Reaching my 4th finger four frets away from the 1st finger was not possible on day one of learning to play. Today, I am trying to reach between frets 3 and 8 at the 5th string. A work in progress, but I see improvement in around 6-8 weeks to where I am buzzing the right note rather than not even close.
I treat the exercise a lot like weight training you would do in the gym. I reach for the chord, hold it a moment, then release. Repeat until I feel fatigue start, then relax and let the hand rest for maybe 90 seconds to recover. I’ll repeat this 3-5 times, then move on to whatever else i want to do. I think this is best done near the end of your session since you leave your hand fatigued. If I over-do it, I may need to avoid this exercise for a day or two so I don’t generate a longer term injury.
There are a couple things happening to your hand doing this: 1. you are improving muscles that generate the stretch 2. you are slowly gaining range of motion by stretching out stuff you probably never used in daily activities before guitar.
Your body adapts, it just takes a bit longer than we may want it to. 
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