Official File retention policy for OneDrive for Business and SharePoint

Items are removed from the recycle bin(s) after 90 days, starting from the original delete date, independently from the recycle bin in which they are (first or second level). Notice that the items do not automatically move from the first level recycle bin to the second level recycle bin. The second level bin is rather an "administrative" bin which is used to recovery items that users have mistakenly deleted from the first level bin. Give a look to this: https://support.office.com/en-us/article/Manage-the-Recycle-Bin-of-a-SharePoint-Online-site-collection-5fa924ee-16d7-487b-9a0a-021b9062d14b?ui=en-US&rs=en-US&ad=US