Warning, I am no expert and this reply is an ersatz to help you direct your researches if no one else comes to post a better one.

Tea got introduced by the English, it was part of their strategy to sell the production from their colonies. The first european trading post along the western African coast were established around the 15th century, so that's your early limit. Not sure exactly when the British did.

As far as I remember, the tea came from China and the trading became important somewhere in the 18th century (similarly to the slave trade). Those incomplete and approximate memories may come from reading "histoire du Senegal" from Mamadou Diouf.

Hopefully someone will come to correct/precise my post.