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  • Kristopher Augsburger thinks this is interesting:

5. How long do deleted site collections remain in the Recycle Bin before being purged?

From

Cover of Exam Ref 70-347 Enabling Office 365 Services

Note

90 days

https://support.office.com/en-us/article/Restore-a-deleted-site-collection-91c18651-c017-47d1-9c27-3a22f325d6f1