How can I figure out the duration of hook_block cache time?

My question is how can i figure out the duration of hook_blo开发者_运维知识库ck cache time and then how can I control it? I want to control the cache settings to get cached every one hour or two hours?

Any idea about this?

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You can check the Block Cache Alter module for that (http://drupal.org/project/blockcache_alter).