Okay I am ready; I am posting my answer here;
Most likely you do not need any Plan B in your case.
You did not have period for many months most likely implies you are menopausal, and also implies you are not undergoing any ovulation now
So you do not have any suspicion for developing pregnancy
Please see that Plan B is supposed to be used within 72 hours after sexual exposure, and in your case the exposure took about 10 hours ago, so you are still within the window period
This means if you do not want to take any chance then you may go ahead and use Plan B
This way you are not taking any risk of pregnancy, however most likely you are not undergoing ovulation as pointed earlier above so you most likely do not need Plan B
Please let me know if you have any further questions, and if you feel you have received the answer to your question please rate me so that I can receive credit for the time and effort put by me in answering your question.