The low stock WhatsApp woke my manager at one in the morning. Can I stop it at night?

Not by time. The low stock warning goes to your managers group the moment a dish's count drops past its alert level, whatever the hour, because it is an order message and not marketing. It is sent once, on the way past, and not again for that dish. If a dish sells out overnight it is because somebody ordered it overnight, so the honest fixes are to raise the alert level so the message arrives during service, to clear the alert level on Menu → Inventory for dishes that do not need one, or to close your ordering page at night under Settings → Working hours. The managers group is also where cancelled after delivery alerts land, so keep it to people who should be woken.