Weekly task - Have 3 sims reading the encyclopedia between 9PM and 1AM.
Here is a classical time sensitive quest. The task has to be performed within a specific time slot, in this case between 9PM (21:00 for us Europeans) and 1AM (01:00).
I started this mission right after 9PM but as long as you do it in the time slot you will clear it.
Call 3 sims to the same house, I used a mix of adults and seniors for this.
Click on a bookshelf and select Encyclopedia. Do this for all three sims and the task should clear directly if you do it at the right time.