Night of Ekadasi / Benefit of Each Quarter

1. During the first quarter of the Ekadasi night the devotee should offer some coconut meat to his worshippable Deity (Isthadeva), 
2. During the second part he should offer soothing bel fruit, 
3. During the third part an orange, and 
4. As the night draws to a close some betel nut. 

http://en.wikipedia.org/wiki/Yajna

1. Remaining awake during the first part of the Ekadasi night bestows on the devotee/sadhaka the same merit as that gained by performing the Agnistoma-yajna. 
2. Staying awake during the second part of the night bestows the same merit as that gained by performing a Vajapeya-yajna. 
3. Stay awake during the third part gives one the same merit as that attained by performing an Ashvamedha-yajna. 
4. And one who remains awake throughout the night receives all of the above mentioned merit, as well as the grand merit of having performed a Rajasurya-yajna.

Source
Padmini Ekadasi, the Ekadasi that occurs during the light fortnight of the extra, leap-year month of Purushottama, from the Skanda Purana.