It'll be fine for a long time. You can leave it at room temperature for a while, if you're brewing soon, but I'd cover it with sanitized foil and stick it in the fridge. If it's a while until you brew again, you can always "wake it up" by adding a little fresh wort a day before brew day. If it's a while, you can also decant off the spent wort after it spends a few days in the fridge, so when you use it, you won't have that old wort in it.
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