Yom Tov is to be divided half for oneself and half for Hashem.
Rav Shach is said to have said over from a Sforim Store owner in Vilna, who heard from the Gerrer Rebbe the Imrei Emes the following.
The Pasuk (שמות כד, ו) says that Moshe Rabeinu took half of the blood. Rashi explains that while it is impossible for a man to split it exactly in half, a Malach came to divide it in half. If so how are we supposed to divide up the day, half for Hashem and half for us, is it not impossible for a human?
He answered that from here we see that on Yom Tov man is like a Malach.
Lets make sure to devote at least approximately half of Yom Tov to Hashem.