Early Quakers saw that the days of the week and the months were named after pagan gods or Roman emperors, so as part of their testimony to simplicity and as part of their Christian faith they started to refer to the days and months by their numbers. So 25th March became 25th day of Third month. Sunday was First day, Monday Second and so on. In Quaker business meetings today you may still find the old practice used but the modern way of dating letters is itself very similar and very simple e.g. 25.3.95, so you are just as likely to find modern Quakers using the modern method.