HaRambam teaches us in Hilkhot Tefillah Chapter 1:1-2-- It is a מצות עשה (positive commandment) to pray every day, as it states: "ועבדתם את ה' אלהיכם, You shall worship the Lord your God" (Shemot 23:25). By tradition, they learned that this worship is prayer, as it states: "ולעבדו בכל לבבכם, and to worship God with all of your heart" (Debarim 11:13)—the sages said what is worship of the heart? This is prayer. The number of prayers is not biblical, the form of prayer is not biblical, and prayer has no biblically fixed time.
Therefore, women are also obligated in prayer because it is a positive commandment lacking a fixed time (מצות עשה שלא הזמן גרמא), but the obligation of this commandment is as follows: a person should supplicate and pray every day and relate the praise of God, and afterwards ask for their needs as a request and a supplication, and afterwards give praise and thanks to God for the good that has been bestowed upon them, each person according to their ability.
(Translation from http://www.sefaria.org/Mishneh_Torah,_Prayer_and_the_Priestly_Blessing.1)
Therefore, women are also obligated in prayer because it is a positive commandment lacking a fixed time (מצות עשה שלא הזמן גרמא), but the obligation of this commandment is as follows: a person should supplicate and pray every day and relate the praise of God, and afterwards ask for their needs as a request and a supplication, and afterwards give praise and thanks to God for the good that has been bestowed upon them, each person according to their ability.
(Translation from http://www.sefaria.org/Mishneh_Torah,_Prayer_and_the_Priestly_Blessing.1)