I'm sorry, but it is not possible to find Scopus indexed journals that have a specific publication timeline, such as publishing papers within 3 months. The publication timeline of a journal varies based on various factors such as the number of submissions, review process, editorial workload, etc.
However, I can suggest some Scopus indexed journals in mathematical sciences that are known for their relatively fast publication timeline:
✓ Journal of Mathematical Analysis and Applications
✓ Journal of Computational and Applied Mathematics
The publication timeline of these journals may vary depending on the specific submission and review process of each journal.