I thought since a lot of people are having a lot of issues finding secrets, and for those who just want to talk about the lore of the map/houses. I thought here would be a good place to talk about such without having to worry about spoilers for those who don't want them.

Starting the quest: Go to the house stated on the flyer apon spawn (house 20), you'll notice that the ground in front of the house is colored differently (look for the sewage grate), break that until you find the time machine.

Quest Part A: Pick up and put the seed in the hole as stated on the sheet of paper, as far as my knowledge goes there is no secrets on this part as to my knowledge.

Quest Part B(QR Code): To my knowledge there's only one secret located on this map and that is in the wheat field; please note that you can only use the tractor in the barn to destroy the wheat, attempting anything else will break the QR Code. Head towards the back middle-ish of the crops and you should eventually find the QR Code.
Now completing the main quest on the map, you'll be looking for a Teddy bear. That Teddy Bear is located in a crawlspace you can find through one of the rooms in the upstairs part of the house.

Quest Part C: Now your primary object is to destroy the old tree. As far as I've been able to find there aren't any secrets on this location but more than likely I just haven't found them yet.

Quest Final Part(Courtroom): You've been teleported back to grandma Betty's house, in the Den you'll find a tree seed to replant complete the message of replanting trees and taking care of our planet. Once you've planted the tree you'll be taken back to Oak Street's Menu. Congratulations you've now completed the quest of Oak Street.
Pssst... Knock over grandma Betty