If I change a price on my dashboard during service, when does the POS see it?

Within about a minute. Cloud based restaurant POS systems keep the menu in one place rather than on each machine, and every paired device refreshes itself from that copy. A sale already in the basket keeps the price it was rung up at, and the next sale uses the new one. The same edit reaches your ordering page at once, so the counter and the online menu never disagree for long. The POS and the counter tab in the docs describes how the devices stay in step.