How to fix the execution time limit of PHP scripts when importing the database in magento?

You need to set the max_execution_time to the number of seconds that all your scripts are allowed to run in your PHP's configuration file. The file location may differ from system to system but in general, you need to find the PHP.INI file and modify it. 

We need to set the Magento max execution time value to 18000.

Here's a Magento import script example:

; Maximum execution time of each script, in seconds
; http://php.net/max-execution-time
; Note: This directive is hardcoded to 0 for the CLI SAPI
max_execution_time = 18000

You'll have to restart your web server for this solution to work.