Heartbeat: is run on a regular interval (you choose) and can do something you define in the heartbeat prompt section of that settings.

Crons: is run when you want, you can ask to Moltis things like "do <whatever> every day at X" and it will automatically create a cron entry, you can disable later.

For cron, what's the difference between "Agent Turn" and "System Event"? Also, is there a way to delete cron runs from the chat list?