The score for the Daily Sudoku is by time, I think, and should also be by level of difficulty and whether you have used any helps. But I can’t see an obvious pattern. My daily top score, and the top ten scores starts over each day at eleven (midnight eastern) but the puzzle for the day is available one hour later at local midnight! Other games don’t work like that.
if I play again the same puzzle, I have to reset it, and my score is zero. This sometimes wipes out my daily high score. Blah! If you missed a day you can choose a puzzle for an earlier day and the score will count for today’s daily high score.
My tip is to use Menu> place notes>whole puzzle, then look for squares with only one candidate. If I see a square with no candidate, I use Undo since I have made a mistake. When I can’t find a move to make, I choose one and go from there until I see there’s an error, or often I can get all the way to the end. If an error, back up with undo to the point of my guess, and choose the other number for that square. Doing the Sudoku this way is fast but is a totally different game than on paper, or placing the candidates myself in the online version.