My LDR girlfriend and I talk to late at night, but it impacts my sleep too much. How do I tell her it gets too late without me noticing?

So me and my LDR girlfriend talks on the phone to late at night, but I need to sleep, although I like talking very much. How do I tell her I need more sleep and can’t talk to her as long as we are now without her feeling like a burden to me?
My LDR girlfriend and I talk to late at night, but it impacts my sleep too much. How do I tell her it gets too late without me noticing?
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