If I have a long list of activity items that takes a long time to scroll through while entering time, how can I limit this list in Core?
Core allows you to assign items to projects as a control measure, which can limit your drop-down lists in the time entry screens. The Project Assignments screen allows you to specify which employees can work on which projects and what activities are allowed for them. So, when you go to your time entry screen, you only see those projects and items that are assigned to you.
To set up project assignment, check Assign Activities to Projects for details.