No disrespect to all poster above but training is constant.
Well...that's your view. That's how you see it, and I know that others like to view their entire existence through the aikido paradigm, where you believe that your every thought or action is somehow aikido training. I don't see things that way, nor do others, and I think that that difference needs to be acknowledged in order for a discussion to be at all useful -- otherwise you've got one person who says "I train six hours a week" and another who says "I train 24 hours a day, every day", when in fact both of them are doing the exact same thing in terms of how they spend their time. I don't know exactly what OP was looking for in asking the original question (maybe just to get an idea of how much time spent in training, oops, I mean on the mat, is optimal), but somehow I don't think it was to find out who could do the best Yorkshireman sketch about their aikido "training".
"I get up and start training at ten o'clock at night, half an hour before I go to bed, drink a cup of sulphuric acid as a form of misogi, practice tai sabaki twenty-nine hours a day as I work my job at the mill, and when I get home, my spouse tests my zanshin by walking into the room unexpectedly as I prepare dinner. Oh, and two or three times a week I go to class."