before I have been
Is the following structure acceptable? What worries me is the usage of present perfect with the preposition "before". On the other hand, I cannot come up with anything better that would convey the same meaning.
We need to leave before we have been here too long.
I have to finish my homework before I have been here for two hours.
Are both of the sentences natural?
I'm not a teacher, or a native English speaker. Feel free to edit my posts if you encounter any mistakes in them (be it grammatical or vocabular). It'll help me to improve my command of English.