25 total fragments from a lv 20 bond Minato.

You shouldn't be able to miss the level checkpoints (5-10-15-20), and even if you exceed it you should still have the mission added to the board, so the only way to "miss" it is to not do it.

Note-I'm sure you already are aware of this, but this system gives Jonin Minato fragments, no Hokage Minato fragments.

Level: 5 10 15 20

Fragments:5 5 5 10