Hi RuiMin,
Office 365 now activates backup data instantly. Microsoft has built in redundancy and backups in all of their data centers, just like Google, Salesforce, etc., but these backups are for internal data center recovery only, and not available to customers for restoring their data in the event of accidental or data loss. Once data is automatically or manually purged from the recycle bin, it will be gone forever.
Regards,
Spike