https://release.k8s.p4.greenpeace.org/international/a-timeline-block-example/
Ticking or unticking the 'Start at end' checkbox in the backend did not change anything in the frontend (tested in Firefox v66)

To replicate:

1. go to Edit page
2. click on Edit on the Timeline block
3. tick or untick 'Start at end' checkbox

Correct behaviour would mean that checking the checkbox would make the last item in the spreadsheet/timeline would be visible by default. Now it's still the first.