www.wysiwygwebbuilder.com

When a visitor clicks on my google website link, is it possible to create a 'temporary' image of one of my items that is perhaps 1-2 seconds duration then fades away to reveal my existing index page? Secondly, will the duration (1-2) seconds vary a lot depending on the power of their computer/tablet/phone?

Do you mean this?
https://www.wysiwygwebbuilder.com/preloader.html

Or else:
https://www.wysiwygwebbuilder.com/pace.html
https://www.wysiwygwebbuilder.com/preloadingscreen.html
https://www.wysiwygwebbuilder.com/loaders.html

This maybe the answer Pablo, but can I use this facility for a FULL page? What I want to display (briefly) is a full page example image of broadly what I make, as the standard thumbnails do not show them in their full glory. Secondly, does the duration of the page differ dependant on the speed of the viewers computer/phone?

Do you have an example?

I meant, do you have an example of a website which implementations this functionality.

Note that it will take some time to load such a large image, so the rest of the website may have already been loaded befroe the image can be displayed...

No good then, but thanks anyway

Maybe a bit late to answer but couldn't this be done as a popup or a layer using onload the image and fade out after say 10 secs?
Here is a jsfiddle with what I think your are asking..
https://jsfiddle.net/davidThomas/Je3wB/1/

Preloader but an image. I think it is possible by optimizing the image and using a layer. So yes it is possible.