The OptomCas application does not open for the fall 2019 cycle until June 2018, which is what they would be uploading their letters to. When you are completing the LOR section of the application you enter in the optometrists or professors email and it sends them a link to fill out an evaluation + send in their letter. Since you still have ~6 months left until the cycle application opens, I think it would be best to start talking about it casually when it comes up and maybe try asking them if they would be willing to take you as a shadow. I say this because in some schools they don't consider working in a clinic as shadowing, but not all schools are like that. Anything to help you gain experience and help give them more to write about in your letter will be great. Then maybe bring it up again in late Spring time that way you are able to add their email into the system right as the application opens in the Summer. Around this time you could also start working on your personal statement essay that goes into all your applications.
Also, kudos for preparing for this so far in advance. That is something I wish I did with my LORs when I was applying. My optometrist letter and 2 undergrad professors just recently submitted their LORs this month and I'm applying for fall 2018.
To give you somewhat of an estimate, a lot of people submit their final applications from October to December in the year before they end up matriculating, so anything submitted before that is considered really early. Typically January - March are considered late in the cycle, as the cycles usually start closing in February, March, April and beyond depending on the school.
I would recommend you start thinking about the OAT and making sure your pre-reqs are all set while you are ahead, that way you can help ensure you get a great score. The OAT, your GPA, pre-reqs, experience, LORs, and essay are pretty much the main pieces to the overall application. Hope this helps!
