The XKCD comic you're thinking of is much more general^: https://xkcd.com/1205/
^ and not too helpful here because it assumes you know how much time something saves/costs - which isn't obvious for spaced repetition because the entire point is to dynamically adjust the timing & number of repetitions over the long run.
The XKCD comic you're thinking of is much more general^: https://xkcd.com/1205/
^ and not too helpful here because it assumes you know how much time something saves/costs - which isn't obvious for spaced repetition because the entire point is to dynamically adjust the timing & number of repetitions over the long run.