Marital preparation courses differ in type and requirement from diocese to diocese. Therefore the timeline will be specific to your diocese and even your parish (some parishes book up a year in advance for weddings, while others do not). So, anywhere from 6-12 months.
Contact your priest to find out whta must be done in your parish.
As for Confirmation, I think people here are understating its importance-- making it sound like it’s no big deal you aren’t confirmed. It is a big deal. It’s an obligation of all Catholics to be confirmed. I am glad you have returned from your sojourn outside the Church. You should talk to your priest about receiving the sacrament as soon as possible. Now is a good time since most adult confirmation classes go on in the spring with confirmation being sometime between Easter and Pentecost.
Regarding Confirmation and marriage, canon law says this:
Can. 1065 §1. Catholics who have not yet received the sacrament of confirmation are to receive it before they are admitted to marriage if it can be done without grave inconvenience.
A “grave inconvenience” would be something pretty drastic.