Defining your flexfield is easy once you have completed and documented your planning stage. You use Oracle E-Business Suite setup forms to define your flexfield.
Depending on exactly how you want to validate your segments, you may spend 10-30 minutes defining each value set (roughly one value set per segment, or fewer if you plan to share value sets or do not plan to use value sets for certain segments).
Note that you do not define your actual values at this point; rather, you are simply defining the containers for your values. See: Value Set Windows.
This is the main part of defining a flexfield, and includes defining structure titles, segment prompts, segment order, and segment display sizes. Depending on the number of structures and segments you have, you may spend 20-90 minutes per flexfield. See: Key Flexfield Segments, Descriptive Flexfield Segments.
Depending on exactly how you want to validate your segments, you may spend anywhere from 1-3 minutes defining each independent or dependent value in an Oracle E-Business Suite form. If you have legacy systems, you may need to build a program to import your legacy values into Oracle E-Business Suite tables. See: Values and Value Sets.
If you plan to use additional features such as cross-validation rules or flexfield value security, you define those additional features at this point.