To increase  max_execution_time  on the staging site, you may try these methods:

1. Edit file  wp-config.php

Add the following to wp-config.php:

set_time_limit(300);

2. Create .user.ini

Add the following to .user.ini:

max_execution_time = 300

You can use the SFTP details of the staging site and connect using FileZilla to do this.