deck cadet seatime required when sailing on oil tankers

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deck cadet seatime required when sailing on oil tankers

hello guys, I am a deck cadet and I have done 7 months on an oil tanker. Please could anyone can tell how much sea time do I require as to appear for 3rd officer's exam? I recently heard that deck cadets sailing on tankers only require 15 months of sea time and not the regular 18 months. Could anyone please help. Thanks.