http://docs.onfleet.com/docs/tasks#list-tasks
CompleteBeforeBefore and CompleteAfterAfter params do not seem to be supported for Onfleet::Task.list.
edit:
Onfleet::Task.list({completeBeforeBefore: to, completeAfterAfter: from}) returns a list of tasks, but it's the same as if the parameters were not passed. Onfleet::Task.list({worker: 'worker id'}) also returns all tasks, not just the ones by the worker. However Onfleet::Task.list({state: 1}) works.