Block time is the time from when a zone is taken until another player can take zone. New turfers block a zone for ten minutes. At most, a zone can be blocked for twentyfive minutes. The higher the ranks, the higher the block time.
In a bonanza event, special rules are in effect regarding the block time.
Block time was modified on 2012-04-01, it used to be your rank multiplied by two. It was, like today, until rank 30. The maximum block time was therefore sixty minutes. The minimum block time was even then five minutes.
On 2016-12-04 the block time was once again changed to the current system.