This is something I’ve been tackling myself in the language app I’m making https://store.steampowered.com/app/3220820/Bilingual_Crosswo.... Right now, I’ve added a set of front loaded intervals: 2M, 5M, 10M, 20M, 40M, 2H, 6H, 1D, 2D, 4D, 8D, and so on eventually stretching to a full year.

I’ve always felt this setup was a bit arbitrary and considered it a temporary solution. Thanks for saving me some time on research!