How long can a dog go without being let out to go to the bathroom?

I'm pet sitting. I let the dog out at 6:30 tonight, what time do I need to let her out again in the morning? Thanks! P.s. she's about 8 years old but very healthy.
Update: The owners just said let her out in the morning, they didn't say when, they just said 6-7 at night to let her out. I'll go again at 10 tonight because that's way too long for a dog to go without going to the bathroom!
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