I've been doing spaced and interleaved practice on and off for quite some time on other instruments, long before I began learning piano three years ago. I find the book-keeping / logistics to be a major hurdle and my main reason for the "off"-periods.
There used to be an Android app called PianoPracticeAssistant which despite being far from perfect has been the best I've found this far. Unfortunately it's not been available for several years and I have not been able to use it since my previous phone broke down in 2021 or so. While I no longer recall all the details of the app, one of its stand-out features was that you had to evaluate and input your "mastery" of a section after each practice instance and the app would use that info to calculate when to come back to that section the next time. In other words there was no strict preset schedule. Does anybody know if there is some similar app available nowadays?
Molly said in a video that she's come to only schedule the very next time for practicing something in her calendar, not drawing out a complete schedule from the get-go. As I see it, a main benefit of this approach is to be able to deviate from the strict schedule based on how easy it was or how well you played, and also if/when to combine small sections into larger ones. Obviously it takes time and experience to get good at such estimates.
For randomised interleaved practice within a single practice session I peruse items from the board-game shelf: usually drawing differently coloured pawns from a bag (with matching marks in the sheet music) and having some score-board to keep track of how many times in a row I play something up to standard and how many times I've returned to each part. That works well enough, but the larger timeframes are cumbersome to keep track of. (Especially when trying to keep up a practice regimen on multiple instruments.) I'm still trying to find a good and low-maintenance system for that. Any suggestions welcome!