Ebook Central ebooks (formerly called EBL) are the only books the library currently maintains that need to be "checked out;" EBook Central ebooks can be checked out for up to 7 to 21 days. Other ebooks that can only be used online can be used at any time, as long as you remain online. eBooks on EBSCOhost allows you to "check out" ebooks offline for up to 7 days. If a publisher allows downloading as PDFs, you may use that content as long as you need it.
Some ebooks are limited to only one user at a time; in these cases, you may get a message that states that the book is in use and that you should try back later. If this happens, you should return later and try getting in again.