Can OctoPrint web interface be turned off during a print?
Assuming the OctoPrint server is running on your Raspberry Pi, which is the usual &quot;OctoPi&quot; setup, then yes, once you have uploaded the G-code to OctoPrint, you no longer need to leave the web interface open.
For example, one could upload code from their desktop running the slicing software to OctoPrint, walk to the printer to turn it on, then use a different device (a phone, for example) to connect OctoPrint to the printer and begin the print. At no point does the device accessing the web interface matter. The Raspberry Pi is in control of the printer, not the device that started the print.