Hello!
You actually had my wheels turning on this one too! This appears to be an Allo only feature. I, like you, was shocked by this. I did some pretty good testing on my own personal device and saw some additional feedback on Reddit confirming this. What makes this horribly confusing is Allo does contain the Google Assistant inside the app. You can type or speak directly to the assistant to achieve your above question. Using the same commands outside of the Allo app will result in nothing.
For example, inside Allo I asked Assistant to "send joke daily." She politely responds back asking for a specific time I would like that alert. I selected my time, and received a notification for it within a few minutes.
Then, I closed Allo, and asked the system Google Assistant the same question. You are not able to complete the same task. I tried a variety of commands with different topics without any luck.
Allo can be found on some devices as a stock app. However, if you do not have it, it can be downloaded here:
https://forums.androidcentral.com/e...le.android.apps.fireball&hl=en&token=uhaXLVtD
Hope this helps!