If you use the official tool today, you will spend hours updating. You will also likely encounter the infamous stall, where the update checker consumes 100% CPU for hours without finding updates.
If you need this OS for compatibility, your best bet is to create your own ISO using the WSUS Offline method. If you must download a pre-made file, verify it against checksums provided by trustworthy sources like the "Heidoc ISO Downloader" (which unfortunately no longer supports 8.1 actively) or archived MSDN images. windows 8.1 fully updated iso
Remember: A fully updated Windows 8.1 is a finished book. It receives no new chapters. But for the hardware it was designed for, it remains a swift, stable, and surprisingly capable operating system. Just keep it off the public internet, or ensure you have a robust third-party firewall and antivirus solution. If you use the official tool today, you