لَا أُنْكِرُ وُقُوعَهُ، وَلَكِنَّنِي أَسْأَلُ عَنْ وَقْتِهِ.
I do not deny its occurrence; rather, I ask when it happened.
The adversative expression “lākinna” redirects the discussion. The first part removes a false assumption; the second identifies the actual unresolved issue. These are not two reiterations of one judgment: the second establishes the speaker's requested information after the denial of an attributed position.
Stopping after “I do not deny its occurrence” would rebut the misunderstanding but leave the question about timing unstated. The additional clause therefore serves a definite communicative purpose and is not empty padding.