You're only completely locked in for the first year. From year 2 through year 5, you can cash in at any time, but lose the last 3 months of interest. After that, you're free to cash in whenever without penalty, or it will be automatically cashed in after a total of 30 years.
https://web.archive.org/web/20221028091214/https://www.treas...
(I'd link to TD directly, but it looks like it's being hammered right now.)