It cannot last that long. PHP script execution is usually hard-coded within the server to stop in 30 seconds or even less. The cron indexing only does one single iteration of 25 items at once ( or as set on the back-end here: https://i.imgur.com/hLRYKVm.png ). That usually lasts like 1-5 seconds tops, depending on post lenght and server performance. It can’t do any harm, as if there are no items to index, it will not do anything, just check.
