I think two days a week isn't too bad. My old dojo was just two days a week and eventually, like you I could stay for an additional hour each day (so I was banking 4 hours a week). In my current dojo, I train four days a week (banking 6 and half hours a week). I am hoping to add another day to my training schedule in the near future.
Just as not enough training can be bad, so too can over training. Some people get burnt out, injured, sick, etc. Each person has their own optimal classes/hours per week that they have to find for themselves. Most people in my dojo seem to train two to three times a week.
Welcome to aikido and best of luck!