Early 2011 MacBook Pro, macOS High Sierra, FileVault Encryption Preventing Bootcamp Partition

I have recently changed out the hard drive in my early 2011 (model A1297) MacBook Pro and installed the High Sierra macOS. On completion of the OS installation I was asked whether to enable the FireVault encryption mechanism. Somewhat foolishly, without conducting the proper research beforehand, I said Yes, and then forgot about it.

Today I went to continue my laptop restoration by setting up a Windows partition using the Bootcamp facility. However this proved impossible due to the ongoing encryption. On investigation, the encryption progress had reached 2.02%. Attempting to deactivate FileVault I learned too late that this was impossible until the encryption process had completed. Over the last four hours the process has moved forward another 0.08%. At this rate i calculate that it won't be complete for another 202 days. This matches the "more than a day" estimate presented in the Security & Privacy section in Preferences. My hard drive is 1TB capacity, of which about 40GB is in use.

Research here in the Discussions forum leads me to believe that I have no option but to wait until November to continue setting up the laptop. Research elsewhere implies that there may be other ways (without having to re-build the hard drive from scratch again).

I'd be grateful for thoughts or ideas on potential solutions to my predicament.