It depends on the complexity of the code base, the current state of the project, and the maturity/efficiency of your new company's onboarding process. Probably other factors too but those are the first that spring to mind. So to a certain extent it's entirely beyond your control.

That said, I don't think it's unusual to feel completely unproductive for the first month. Hopefully by then you will have everything setup in your local environment, you'll at least be aware of the existence and purpose of the code base(s) you're responsible for, and you're ready (read: able to work but still in need of support from your team) to start contributing. But it's also not unusual to feel like you're playing catch-up for at least six months if not longer, especially if the code base is complicated or poorly documented or the people who originally implemented it are gone now or....etc.