Set aside a time each day (give yourself a break from the routine one day per week) for work with the Leitner Boxes. More time will be required as we get deeper into the subject. Same time each day is not required. This is a thinking activity, with respect to thinking the brain cannot multitask.
When retrieval practice is spaced, allowing some forgetting to occur between tests, it leads to stronger long-term retention than when it is massed. The advantage of spaced practice was first observed by Ebbinghaus in 1885 and no study has ever been able to refute it. Delaying subsequent retrieval practice is more potent for reinforcing retention