After the students have fully understood the text, this would be the best time for them to discuss their opinions on it. I changed "it" to "this" because "this" is more appropriate when referring back to a whole phrase rather than just a particular noun. I changed the second "the text" to "it" because it feels more natural to replace the repetition of the noun with a pronoun.

Hello, this sentence is correct, however it could be improved by ending the sentence: discuss their opinions on it. It is good to use 'it' to refer back to the text in the first part of the sentence. Jacqueline