我在PHP中有一组类似这样的数组。

["Monday"]=> string(7) "8AM-4PM" 
  ["Tuesday"]=> string(7) "8AM-4PM" 
  ["Wednesday"]=> string(7) "8AM-4PM" 
  ["Thursday"]=> string(7) "8AM-4PM" 
  ["Friday"]=> string(6) "Closed" 
  ["Saturday"]=> string(7) "8AM-4PM" 
  ["Sunday"]=> string(7) "8AM-4PM" }

如何将小时数转换为24小时制？