First there is always time, it really depends on how much you want to do optometry. I'm not sure how many pre-reqs for opt school you've done with your cog sci major, but if you can't plan out the required classes that you need until you graduate, then you should consider taking classes over the summer, or a year off.
Find out more about optometry. If you get the opportunity, try to shadow or observe at an office to get a feel for what it's like, or talk to your own optometrist. At least you'll get your feet wet and see if it's worth pursuing.
So, first try to plan out how you'll finish all the pre-reqs. Some schools will allow you to finish pre-reqs after you're accepted, but try to keep that to a minimum because you don't want that to hinder your chances getting into a school.
Next plan when you're going to take the OAT. Berkeley has a rough timetable of when you should get things done. Their deadline is the earliest for applications, so I went off their timetable. Other schools will accept applications earlier too.
http://spectacle.berkeley.edu/opt_txtpp/admissions/admittime.html
You might want to sign up for a prep course, too, if you need it.
Also start finding professors and an optometrist to write recommendations. This is where shadowing/working/volunteering at an office comes into play because the more time you spend with an optometrist, hopefully they have opportunities to see your strengths and understand why you want to do optometry. Also make sure these people can write strong recommendations.
Find the schools you're interested in, and their application deadlines. This will help you concentrate your efforts on meeting the requirements for those schools and not wasting time on others.
Hope this helps.
I decided on optometry the summer before my 4th year after shadowing. But my major already covered many of the required classes. I am currently taking a year off and working at an office, and have been accepted by SCCO and waiting to hear back from Berkeley. Other applicants, I've met are 3-4 years removed from undergrad, and they decided to pursue optometry. So, it really depends on your drive and interest for this career choice.
