Multi-Fandom Fan Fiction

I don't know if this is the best way to contact you but I figured I'd try this first. I was assigned a Supernatural fic, however I've recently come to have some misgivings about the couple and don't feel that I can post the story I have done. In light of this I would like to do my runner-up of a SGA/Firefly crossover. If I could possible have a week or two extension I think I would be able to create a well done fic. If this is acceptable please get back to me as soon as you can. Thank you.