Good old Midday Prayer with the name which becomes a little awkward in English. Sext means the sixth hour after sunrise, which is midday or 12 noon.
Funnily enough, the English word Noon comes from the next hour, None, referring to the Ninth Hour. This was the hour at which monks would break fast, but over time it was felt to be too onerous to wait that long, so they started breaking fast at the Sixth hour, but the name None carried across and now we have Noon being the middle of the day.
As always, you can find the booklets at https://littleoffice.brandt.id.au/#booklets
Sexta Adventu - Office 2