Passage: A tsunami warning was issued in Palu and Donggala at 18:07 WITA. Warnings were sent via SMS by the Indonesian Ministry of Communication and Information. Residents of Donggala were told to expect tsunamis with heights of 0.5 to 3 metres, while residents in Palu were told to expect tsunamis with heights of less than 0.5 metres. The tsunami, however, struck higher than expected. Residents of Palu reported waves with heights of more than 2 metres while several others stated that the waves managed to reach the second floor.Indonesian officials calculated the estimated time of arrival of the tsunami. Calculations suggested that the tsunami would arrive in Palu approximately 20 minutes after the earthquake. Around 18:27 WITA, the Indonesian meteorological agency (BMKG) in Mamuju detected tsunamis. A tsunami warning was issued, and later lifted. The BMKG claimed the warning was lifted after the tsunami had struck, but the timing is unclear, and the agency was criticized on social media.Even though officials did send warnings via telephone and television, tsunami alarms were not activated. The Palu Nomoni Festival in Talise Beach  continued and most of the festival attendees did not realize that there was a possibility of a tsunami. Eyewitnesses even stated that some people were still strolling on the beach when the tsunami struck. It was estimated that hundreds were caught off guard and swept away by the waves.The Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) later admitted that the tsunami detectors in Palu were damaged in the earthquake. The shaking was violent enough to damage the tsunami detectors in Palu, as further examination revealed that none of the detectors were able to send signals to alert residents.As Palu was located at the end of a narrow bay, the tsunami's force was intensified when the waters entered. Officials confirmed that the waves that struck Palu had actually reached a height of 5 metres, with some as nearly as high as 6 metres.The tsunami caught geologists by surprise....

Question: When would the tsunami arrive according to calculations ?
20 minutes after the earthquake