I doubt that having a small cup of tea before the 2-hour cutoff for water would pose a significant risk.
A user here recently had 1 herbal tea during the food fast (before the water fast) and it was a success. As long as you're not adding cream, sugar, honey, or anything else and keep to that small cup, you should be fine as long as you avoid all fluids for 2 hours before ingesting the SN.
That said, it's important to carefully consider any additional variables and choose what you believe is best for you after evaluating everything. Do I think it poses a significant risk? Not really. Would I personally take that risk with something so important? Also no.
Another point to consider is if you enjoy tea in the morning and evening, wouldn't there still be a reasonable window to enjoy your tea in the AM or PM while allowing for a proper fast? It's something to think about if it's truly important to you. Personally, skipping something in my normal routine feels like a very minor tradeoff when I'm already making significant changes for the sake of a successful CTB.
With whatever you decide, I hope you find everything you are looking for and find peace & serenity.
