The sentence "There are thirty minutes free for me before school" is understandable, but it is not entirely natural. Here's why: "Free" vs. "to be free": The word "free" works fine as an adjective here, so there's no need to change it to "to be free." However, the phrasing could be smoother. Pattern "there be + noun + adjective": This structure is grammatical and can be used in English, but it's not very common in conversational English. People tend to use simpler constructions. Natural Alternatives: "I have thirty free minutes before school." "There are thirty minutes when I’m free before school." "I’m free for thirty minutes before school." These options sound more fluent and are commonly used in English.

I don't think is wrong, but it's not very natural. More natural would be: I have thirty minutes free before school.