Send straight away - a swap gets caught. Every lock anyone publishes is written into a logbook that can only be added to, never edited or erased. Your own devices read the page about your account every time they start. If a lock is ever published in your name that your devices did not make, they tell you, and the entry stays in the book where anyone can point at it. A swap can be attempted; it cannot be attempted quietly.
Sending straight away is what every conversation gets. Checking first is the extra step, and it is only worth turning on for people you can realistically meet or ring.
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{who} has not set up encryption on any device, and a locked message needs a key on their side to open it. Messages here are stored the ordinary way until then - it switches on by itself the moment they open OrangChat on a phone or computer.