Timeline for Implementing UX Process

I am in the process of presenting and implementing a brand new UI/UX process. I have gotten buy in for the proposed phases of the design process. But I am getting timeline questions regarding how long it would take to implement the full process or how much could be done within a 6month window and how to plan out a 6month window. I know this is super subjective but has anyone had any experience with anything similar? Or how long each step in a design process could take to nail down/implement?

Thanks!