[ETA: Assume that you are the only one who gets to see the impact estimates, and that you have sworn not to directly leak any of the information you have.]
For instance, you might get impact estimates for:
Running X student group for a year
Helping make X internship, bootcamp, workshop, or retreat happen
Making a youtube video about X that gets Y views
Giving X book to Y person conditional on them Z
And every other meta-EA intervention you have considered/thought of
[ETA: My thoughts here are very very tentative, and easily changed by a new consideration/datum being pointed out.]
Apparently, the Open Phil meta team was surprised by how flat the distribution of impact they measured was, and the distribution seems to only span 2-3 OOMs (importantly, this rough OOM range isn’t for impact per person, which is what you would want, but the total impact of meta-EA interventions that seem like they deserve their own bucket). Though my guess is that unless you have an exceptionally good/obvious personal fit for something, the personal fit consideration leads to 0-1 OOMS, and if this is true, then it is still worth figuring out where the new projects you are considering lie on the impact distribution.
Gut-estimate: 60 days, with a 95% chance that my gut-estimate would be between 2 and 600 days if I thought about/investigated this for another day.