The retrospective and sprint planning are supposed to be much longer than that, and not timeboxed, as far as I know. Also one of the core ideas of Agile is ada

The retrospective and sprint planning are supposed to be much longer than that, and not timeboxed, as far as I know. Also one of the core ideas of Agile is adapting to suit your team, rather than following some process from a book as if it were written in stone. If time limits on certain meetings are causing your team more grief than they help, remove the timeboxes! Talk to your team and see what they think, that's what the retrospective is meant for.