What's a reasonable target(time wise) for gaining 10 kilos?

I’m a healthy male in his late 20’s, and intend to put on 10-12 kgs (25 to 30 pounds) of muscle mass. I’m about 10 kilos under my ideal body weight, my body fat percentage is in the 17-20 % range. I have a very high metabolic rate. I eat a lot, but rarely put on weight, and lose it even faster. Assuming a larger diet and exercise, how much time should I target for putting on 10-12 kilos? 6 months? A year? This is in GQ in the hope of a scientific answer which need not, obviously, be tailored to me, but gives me a ballpark and rules with which I can play.

A lot of it will depend on your genetics and body type. It might not even be possible. Unless they decide to take steroids, putting on 30 lbs of muscle mass would take your average person years to do. You can probably gain 30 lbs in a year by simply eating more, but gaining 30 lbs of lean muscle mass is a different story all together. It’s just a guess, but I’d say 10 lbs/year could be a healthy rate.

Ok, but are there any studies along the lines of, picked 50 males at random, put on such and such diet and so much exercise, 1/2 gained x weight in y time, nothing happened to 1/4th of them, 1/4th gained z weight in y time. I think they have studies like that for weight loss.
Also, I have in the past been able to gain muscle mass (approximately 5 kgs in two-three months) when I work out and eat a lot, but it all goes away within a month if I stop working out and eating extra heavy meals. So I know I can gain the weight, I want to be more scientific about it and try and keep it on for longer.

How do you know all that mass was muscle? What kind of a workout were you doing?

I was working out 5 days a week, with free weights, doing two days of chest/back splits, two days of shoulders/arms and one day of legs, 3 exercises each muscle group, interspersed with rest days (IIRC).
How do I know I put on muscle? My body fat percentage dropped a little, but the measuring equipment I was using wasn’t the most accurate. The visible results were what led me to believe it was mostly muscle. No extra fat accumulated anywhere that I could tell, and I got stronger overall. I freely grant that the extra weight may not have been entirely muscle. Hence the desire to be more scientific about it this time around.

Can you deadlift 500 lbs? If not, focus on that. The muscle mass will follow.