Please note that this is just pure headcanon. Don't take this as fact or truth.
Piranha Plant woke up at 8:30 AM. It proceeded to the Smash Mansion's Garden, which was outside the Mansion. Piranha Plant likes to go outside to the Garden for 1 hour in the morning and 1 hour in the afternoon to chomp out any pests that may kill the plants in the Garden.
12:00 PM
It was lunch time for the Smashers in the Mansion. While most Smashers get the regular "human food" meal, Piranha Plant usually gets a leaf salad, garnished with numerous bugs. Lunch in the Mansion usually lasts two hours due to the large amount of characters in the roster. The table is very large too, it has spaces for every smasher, including the actual Pokemon Trainers, Koopalings, both gendered villagers, and both gendered Wii Fit Trainers.
2:00 PM
It was free time for the Smashers and lunch time for the assist trophies, but for the sake of this Fanfic, we'll only focus the Smashers. During this time, Smashers may go to gym to train, battle in the battlefield, or just do whatever they please. Piranha Plant, however typically likes to sleep outside. While sleeping, it doesn't like to be disturbed while sleeping, and some of the Smashers learned that the hard way. When woke, it like to chomp some sense into the Smashers, and may even spew out poisonous gas.
4:00 PM
It's still free time for many of the Smashers, and Piranha Plant goes back to the Garden to rid it of pests once again.
6:00 PM
It was dinner time for the Smashers and Assist Trophies. Piranha Plant typically gets the same salad it usually gets for lunch. Like lunch, it lasts two hours, due to the large amount of characters.
8:00 PM
It's time to get ready for bed in the Mansion. 10:00 PM is the time every Smasher should be asleep and Smashers aren't allowed to leave their room after this time unless if they're going to the bathroom. Piranha Plant is on the DLC floor of the Mansion, which is the sixth floor. Piranha Plant and Joker are the only ones that are on this floor at the moment, but that will change once the other DLC fighters come to the Mansion. Piranha Plant typically goes to bed at 9:00 PM and Piranha Plant's day is over for today.