George S. Ledyard
on the mat every day, 6 - 8 hours a day every day for years.
How many dojos can one find this level of instruction? Where I train there is offered 12.5 hours of instruction per week plus some 5 hours kids/teen classes. Compared to many others it is quite a full schedule (one instructor for all). Previously I trained where there were ~19 hours per week of adult instruction. Besides Hombu and the Yoshinkan I have not heard of anyplace that offers anywhere near 40 hours per week of instruction. I'm not saying there aren't any but they are few and far between.
Granted, serious students make the effort to get themselves to where the instruction is to be had but the rest of us would still rather train than not so we get the best we are able. Does aikido suffer because of us 'slackers'? Maybe we do not make a direct positive contribution (besides the support to the serious as mentioned) but I like to think we do no more harm.
I guess the real question needs to be is two days a week enough for what the OP wants to get out of aikido. If they want to be better than Mr. Ledyard than no but if they want to be help support their instructor and a few serious students along the way then the answer is yes. Just so long as one is honest with themselves and others about what they are doing then two days may well be plenty.
Just to be selfish I'll mention that if I'm able to get 5 hours a week I feel I'm barely treading water. Even with that meager schedule my family suffers due to my selfishness. They may think I'm a serious student but I know I'm not... by a long shot. Even at my most 'prolific' moments I can barely sustain an 8 hour weekly rate. Got no family and are under 30 then get it while you can because life has a way of getting in the way of the way.