Following MetalMunchers prodding, above, and despite what I said, I decided to have a look at what settings can be changed.
I discovered a number of things. Firstly, that as I suspected i had no idea what most of the variables were, or at least what effect they actually had. Secondly, I found that it is easy to set up a new print profile
and retain the original one, which relieved my mind more than somewhat.
I then went to the Anycubic support and looked at their recomended settings for their grey resin and compared them with the basic default settings that Chitubox has been using for the Photon-S. One thing jumped out at me and slightly put the wind up me, the Chitubox lift speed is 180mm/sec and the Anycubic figure is 3mm/sec! Not only is that a huge difference in itself, but it would increase print times by a factor of nearly 90!
So I went off looking at various forums and found a post by somebody who says he routinely uses the grey resin and has good success with various settings which he listed, the important ones being the exposure time of 16.5 sec compared to 8 seconds previously, and the lift speed of 30mm/sec. I found various other posts suggesting lift speeds in the 30-40mm/sec region, which gave a bit of confidence.
So I bit the bullet and copied his complete set of parameters as a new print profile, re-sliced it and pushed the button. It took 24minutes to print what was previously taking 11minutes, but it came out perfectly first go!
Of course these thin sheets are only 1.25mm high so quick to print by any standards. Anything very tall would start adding very significant time to the print, so I don't think I shall change to this as a default, but I might play around for a compromise. The thing is that it is only a couple of clicks to switch between saved profiles at the slicing stage, so no problems there.
Thanks for the prodding Richard.