I've written some historical fiction, so I think I can comment with reasonable intelligence on this.
One of the tricks with writing historical fiction is to smoothly balance the comfort and pleasure of modern readers with accurate representation of the time you're portraying. It can be very difficult to find the right compromise between contemporary language that will make a book flow smoothly and appealing to the immersion in a historical setting, which is why fans of the genre read it.
Ultimately, you have to do what feels acceptable to you and don't worry about it too much until you're in an editing phase with a professional editor, who can give you better input on your particular piece. I've read historical fiction where the ultra-modern language was just too much to swallow and it made the entire book seem silly and trite, and I've read historical fiction that tastefully used some modern conventions but still went plenty heavy on the historical detail, and it felt flawless. Go with your personal comfort zone for now, but be willing to revise it as needed further down the line.
Personally, I would avoid using unique, stand-out words that have very modern connotations such as "jockying," unless you can verify that they have etymological roots in your time period. More subtle modern uses such as contractions in speech are much easier to get away with and may help the flow of your work. You can pretty easily figure out the etymology of most words using Google...and it's fun to do!