Where are you located? Does the area get sun or is it shaded?

North East. Mostly sun.

How much can you spend? You can hire outdoor temporary flooring.

Price varies. What kind of temporary flooring?

Here are some suggestions using chipped shale gravel:

How big is the yard? How 'presentable' is 'presentable'? What are the long-term goals for the space?

Coil up the hose, and put it away. Pile the slate neatly in the corner. Find some dirt from somewhere, and fill in the hole near the paving. Mow the grass. If you intend on grassing the area over, I'd get some grass seed and straw. It's the wrong time to do it, and will probably be a total failure, but it will look like you are doing something, and it isn't expensive.

I associate the temporary flooring Flora is talking about with backyard weddings. So if that sounds like something you'd like to look into, talk with local people who rent out event tents.

Temporary can mean many things depending on your budget. The photo below was a temporary display built on a convention center floor:

Thank you for the suggestions and comments. You have provided me with good ideas and I have a better sense of where to get started.

Do you need that area for hosting people, or will it only be viewed? If the latter, clean it up, put down a roll or two of sod and put a big tub of annuals in the corner.

Do clean it up, but The space is so uneven and with the stumps, bricks etc. do you need to use this space? Is there another part of your yard you could host the event?

Look into renting something like a temporary dance floor, perhaps?