Hi kaliyuga,
to get one image at a time, you have to modify the loop in the colab accordingly

for top_k, top_p, images_num in [
(128, 0.95, 1),
]:

I just tried it and it produce a picture after 21 minutes (free version) on a 12Gb gpu.
I have to run some other tests but i think here it produces a 128*128 sized picture and upscaled it.
here the result :

Note: the colab use the Malevich model (XL) = 2.6 Gbytes model, i don't think the XXL can run under free Colab, presumably it would go Out of Memory.
I saw on the github another notebook, allowing to put some init images as prompts... Will explore further when i have time.