Greetings Martin - At room temperature and in a sanatized environment, you should be fine for another 12 hours assuming your starter is only 24 to 36 hours old to begin with. But I would re refridgerate if Its not going to be used within the next 12 hours or so.
I almost made the same disastrous mistake with my kettle valve. But only lost a very small amount before I noticed. Arg!!!
Good luck!
