Yes, that's the correct link.
You really want to try to get the timing right the first time. If you have to send for a new vignette, you have to resend the passport back to Sheffield, wait for it to be processed, and wait for it be to returned. And it costs $253 without shipping.
Basically, you'll still have little control over when the vignette is reissued.
You can apply for travel up to 90 days before you want to travel (so an application today could be dated for traveling in November). Would that be a better option?