It depends on how far an important competition is from the training day. If the competition is close, be careful of too much volume.
I combine speed endurance and special endurance with success - 250m, 150m, 110m, 80m. OR (Kitkat’s example) for a 400m athlete -300m, 250m, 180m, 150m, 120m. (Sometimes it was 260m, 180m, 160, 140, 120).
Furthermore - if your focus is SPEED endurance, I would do it the other way round … e.g. 80, 120, 180, 260.
Good luck with the coaching/training!