Crewing is guesswork with a spreadsheet. Guess short and you stand in the sun for three hours; guess long and your runner arrives to nobody. These are built from what actually happened on each course — the arrival window is the middle half of real finishers who ran the same finish time as yours.
We do not say which checkpoints allow crew access. We do not have that data, and inventing it would send somebody to a place they are not allowed to be. Check the race's own athlete guide, then use these times.