1) If you can take time off from online school without having your education impacted then do so. But if you will fall behind, then pray after school ends.
One recommendation is to alternate. Some days pray on time, and some days pray after school. This way you won’t regularly delay your prayer every day, and you won’t skip class everyday.
2) Yes you may absolutely do that. That would be highly recommended. Pray Dhuhr first then Asr after class ends.