V3 Intraday API - Delayed

Does the V3 intraday API guarantee live updating of candles at the end of each interval?
If yes, what is the expected delay in new candle availability after interval end?

Is this endpoint intended for live streaming use cases, or should we use a different WebSocket

You need to use WebSocket to get live data. Intraday API is cached as per my knowledge so you will not get latest candle after it completes.