Panel 1: We start things off with what looks like a landscape in a mountainous area.
Panel 2: When Steve looks down at what he sees and calls it "Amazing", we quickly realize that we're looking at John's model train layout.
Panel 3: When Steve compliments him on the layout and asks how long it took him to build it, John says that he did the basic stuff in a week.
Panel 4: He points to the table he has it set up on and says that he'd set the base structure up on Monday.
Panel 5: Tuesday was spent painting the wall to look like a sky.
Panel 6: Wednesday was spent on making the HO-scale mountains and river bed.
Panel 7: On Thursday, John put down the (artificial) grass and model bushes and figured out how to make trees.
Panel 8: He then sets himself up to get slammed by his 'supportive' wife by stating that on Friday and Saturday, he'd put down some people and animals.
Panel 9: Since this is sort of akin to Genesis, Elly's 'witty' rejoinder of how on the Seventh Day, John rested allows Steve and Anne to laugh heartily at John's expense.
Summary: Where it falls down is that Elly finds this funny for a different reason. Steve and Anne are having a good chuckle because John doesn't realize that he's accidentally made himself sound as if he'd parted the Heavens and the Earth. Elly is laughing at something she doesn't care for or understand.