Is it safe to change max_execution_time to something like 300? Why magento 2 need this gigantic max_execution_time (18000 = 5 hours) first place?
Yes you can you need to increase execution time so that magento can interact with database easily. It required increment because magento also run many heavy task in background like: product import and export, backup creation, backup roll back and many more so in order to make all process smooth we increase execution time in php.ini file.
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