There's very little data, so I hope you decide to experiment anyway.
For me, 25 minutes using the non-optimal instant coffee+lye+baking soda recipe and Ilford MGIV RC. I liked the stain (Maxwell House Instant Dark Roast), but times were too long for hanging out in my tiny bathroom so I only tried it a couple of times. I used bulb exposure with a makeshift contact proofer, so I can't speak to potential print quality, but I didnt' find my results grainy or dirty.
I found very low capacity. I wonder if the long times have to do with rapidly declining potency and larger quantities are called for.
I've heard of people adding vitamin c.
Some say it's the many organic compounds in coffee that make it a developer, so maybe freshly roasted, ground and brewed coffee would be more effective than instant.