I found my answer on Google’s Moving Your Site page.
To prevent confusion, it’s best to retain control of your old site domain for at least 180 days.
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=83105
Due to circumstances beyond my control, my WordPress installation broke down. I did a fresh install at the other domain, imported my WordPress database and files, and set up the 301 redirect. Everything is working smoothly. I’ll be keeping the old domain for another year before letting it expire.
Thanks for the other answers!