Dioraysa or Dirabanan
Step 1
The Mitzvah is to say Shema with sunrise so that you are able to connect Ga'al Yisroel to Shemonah Esrei
According to Ramban, the mitzvah of davening everyday is a Dirabanan.
Ramban understands from Rambams source from the Pasuk
We learn in Brachot the Halacha if someone has doubt whether they said kris shema. The Halacha is that is someone forgot if they said kriyas shema they need to repeat it because it is diorite. However if you forgot if you said shemona esrai you don't need to repeat because its dirrabanan. This implies that if its dirrabanon( mitzvah from the rabbis) you don't need to repeat the tephila if you forgot if you said it.
Rambam says that we need to pray to hashem every day but there are three exceptions. The three exceptions are when the torah does not say when, how many times, and what you need to say.
According to the Rambam in Hiloshos tephilah in order to fulfill the mitzvah Dioraysa of tephila all you need to do is Daven for 5 seconds and that fulfills the mitzvah for you on a torah level.
Times of day to Daven
Tana Kama: You can say shacrit shemonah esrai till the middle of the day.
Rabbi Yehuda says until the 4th hour of the day
Tana Kama: You can say mincha until sunset
Rav Yehuda says you have until plag hamincha
Tanah Kama: Maariv has no set time and for massif you have all day.
Rav yehuda says you have 7 hours
ולעבדו בכל לבבכם -You should serve Hashem with all of you heart
Sifri: The obligation to pray is because it says to serve god with all your heart and the main mitzvah is that you do with your heart is davening.
Rambam: This pasuk proves that the obligation of Shemonah Esrei does come from the Torah
Dirabanan: How many times to say it, when to say it, what to say. Dioraysa: Daven everyday
