Users of Treasury of Daily Prayer will need to make the Great Skip in preparation for devotions on February 17th, Ash Wednesday. With the beginning of Lent, the Daily Lectionary changes from using calendar dates to using liturgical days. This handily accommodates the changeable dates of the festival half of the Church Year, which are all based on the date of Easter.
So, long story short: February 17th, move your bookmark from the back of Treasury to page 24 in the front. And then carry on.
(There is another Lesser Skip that happens at the conclusion of the Season after Easter, but well remind you about that in May.)