I don't think Snapchat/Whatsapp has any sort of scheduling features, just sending pics and video to groups of people.
From what friends have said, FB groups features (scheduling, etc.) are what keep them on that platform, along with messenger.
One group I'm in, entirely devoted to online games, has switched to Discord. But there is a 0% chance Discord will be adopted by the rest of the groups/friends that use FB event scheduling and messaging.