It's strongly advised against leaving a candle unattended for any period of time, including 30 minutes. Candles are a fire hazard and can cause accidents if left unattended. The National Fire Protection Association (NFPA) states millions of dollars in damages are reported each year due to fire. Therefore, it's crucial to always monitor a lit candle and extinguish it before leaving the room, even if it's just for a short period. Safety should always be the top priority when dealing with open flames.