I've been doing Judo 6 1/2 years (brown belt) and BJJ 4 1/2 years (3 stripe blue belt). I used to train 2 x Judo + 2-3 x BJJ + 1 x Karate a week, but have cut back to 1 x each per week this year due to saving $ to buy a house. To improve you really need at least 2 x a week in each style. 1 x a week I don't feel like I'm improving now, just keeping the same level.
Anyway, I feel very comfortable in standup situations at BJJ, even against bigger or higher ranked guys. I also feel more comfortable in ground situations at Judo. Judo guys tend to be a bit more aggressive and strong, I guess coming from the explosive nature of the sport, so strength is a bonus. Judo guys tend to turtle up and give their back too easily on the ground. Doing both is great, I love it.
As for time to black belt in Judo, fastest I've seen is about 5 years. That would be training 3x a week and regular competitions. Average is more like 7-8 years. I hope to get there in 10 years lol.