When answering this question, I said that the manual and automated roles can easily be mixed. I’ve never been in a specialist automation role, and not sure I’d ever want to be. The amount of time I dedicate to either varies depending on the current team and what work needs doing.
However, if setting up an entire framework or working on a bigger automation task in general, you’ll need to spend a significant amount of time on this. So, you’ll need to speak to your team about allocating time and arranging for someone else to pick up the slack on other testing tasks. You may find you’ll need to temporarily spend 100% of your time on this.
Once everything is setup, general maintenance of the automated tests may not require 100% of your time. Not all tickets that you work on will require work on the automated tests, but you should have that discussion when refining each ticket. If updates or new tests are required, include this in your definition of done. You could have both the manual testing and automated test updates done by the same person or you can split the task between 2 testers. It depends on the ticket, and the skills of the tester.
If splitting the work between 2 testers, you still want to speak to each other. Discuss what changes need to be made, and how best to implement them. If the tester in charge of manually testing the ticket lacks experience in automation, this is a good learning opportunity for them. Get them involved, show them what you are doing, do some pair programming.