This paper asks if there is an optimal wait period for e-books that balances libraries' desire to acquire books soon after their publication with the frequent desire to purchase books electronically whenever feasible. Analyzing 13,043 titles that Temple University Libraries received on its e-preferred approval plan in 2014-15, the author looks at the delays from the publication of print books to publication of their electronic versions. The analysis finds that most books on the approval plan are published electronically within a week of the print. Recommended wait periods are provided for different subjects.