Really depends on your tech and how many projects your team works on. My first job out of college was at a large investment firm. We had 2 projects that we were in charge of and then 1 project thar we supported another team with. So it was really only learning 1 backend service and 2 frontend code bases. I was already familar with angular and typescript so it was easy to pickup. My current job I work on the networking team for a cloud computing company. We manage all the connectivity between the virtual machines, the hypervisors, and the rest of the datacenter. We have so many programs that we maintain inorder to maintain our network that I am constantly working in a new code base I have never seen. We use golang and technology like chef which were both new to me. I also don't have the greatest networking knowledge so getting up to speed has taken much longer than when I was working in web dev.