Right behind the ovens at The Party Tree in The Shire is a door to the cellar beneath Bilbo's house at Bag End.
You may now enter the Haunted Burrow anytime you like. Of course, finding your way out again is another matter...
Within the burrow are four treasure chests which, when opened, will yield tokens, masks, and other Harvestmath goodies. Opening a chest places a 1 hour "debuff" on you which prevents you from opening the same chest again until the timer expires.
An excellent map of the Haunted Burrow can be found here at casualstrolltomordor.com
The rest of the Burrow quests, both timed and untimed, are now open to you. They can be repeated once per day.
In each of the four Festival areas, once an hour you can open a box, bob an apple, pick a pumpkin, or crack open a geode to find goodies. These can be bartered with a Games-master for Festival Tokens.