Are never annoying.
Because either someone is reminding you of something you want. And that’s a good thing! You’re still in time!
Or you see it’s a reminder in the mail subject and you can delete it without opening it because you aren’t interested.
One thing we need to keep in mind and that’s the time people can still use the offer. Because if you remind only an hour before the deadline, people might miss it.
Instead, remind people a couple of times but at least 2-3 days out.
People need to think about what you offer and moreover they need to take action which takes time and effort. It’s your job to make it easy and smooth to take action and remind them in a timely manner.