The plugin “Exact Time Price Rule” is the extension for Magento.
It is the simple extension that allows
administrator of the Magento store set the exact time for price rules in [ Admin Area ]: Promotions -> Shopping Cart Price Rules -> Choose one price rule | or Create one.
When you are using the core Magento functionality you can set the the “from date” and the “to date” parameters when the price rule is active.
When you are using the “Exact Time Price Rule” you can set the exact time when the price rule is active.
“Exact Time Price Rule” also allows you to choose the day(s) of week for the price rule when the rule is available.
1) First of all You should disable Compilation here ([ Admin Area ]: System -> Tools -> Compilation )
2) Then You should disable the cache
3) Unzip the archive with the extension
4) Be carefull when uploading the content of the archive by ftp in root folder of your Magento, You should MERGE the content.