I take this info on their website to mean that if I buy a ticket and pick May 14 as the date, I could go between May 14-20.
"Standard admission tickets are valid for one visit seven days from the date selected. Tickets cannot be resold, exchanged or refunded."
Am I interpreting correctly?
Yes, the linked site says "tickets are valid for 7 days from date selected".
We purchased our tickets when we arrived at the Tower in July 2014, and I do not recall a long line. We got there early, and I seem to recall that the line to enter was longer than the line to purchase tickets. Seems like a good alternative if you are worried.
I bought my tickets ahead of time for May 12, and the voucher says they are valid within 7 days from the date chosen. BTW, your two choices for delivery are for them to physically mail the actual tickets, or email you a voucher. I didn't trust the mail, so I had the voucher sent. I still have to go to the group sales ticket window to pick up the tickets.
I visited in August and bought my ticket at a kiosk near the Tube exit, as Rick's book suggested. No line, perhaps a short line to actually enter the Tower grounds.
