Re: Is two Days a week enough?
I would say if you like that dojo, if the teacher is a good match for you, if it's convenient for you, etc., at least start there for the 2 days a week they are open. See how it goes. Since everyone will be training at that same rate, you all should be progressing at relatively the same rate (unique abilities aside). And as others have said, some of your training can be off the mat, too. If you find you are yearning for more, perhaps (if enough others are, too) you could ask for an additional class or open practice time. Worst case, you could look for a new (or additional) dojo.
When I started I only went one evening per week. That expanded to the point where now I am very happily training 4-5x/week. I'm just very lucky that my dojo offers so many classes.