Thanks Kris.
I also realised tonight, that I can create a bookmark in my browser straight to the theme “Preview” using the URL:
Where yy is the theme number. I got the URL by right clicking on the preview button and copying the link. This allows me to open the forum using my unreleased (in development) theme.
It’s also a faster way to get other staff to check it out, rather than telling them to click: ADMIN>Customize>theme>correct theme>preview.