How long between feeds?

Stop with the top ups. That’s most likely over feeding baby and can easily decrease your supply.

You definitely don't need to be topping with formula at all. If a newborn is going 4 hrs and you're having to force a feed you're overfeeding. Nurse until he's settled. There is no time limit to nursing. Baby should stay on breast until they are completely done and if they aren't satisfied with one side switch. Baby will let you know when they want to nurse if you hold off on the formula.

Topping up with formula is such a slippery slope. It leads to supply drops and overfeeding. If babe is acting still hungry, keep offering the breast. You always have milk and they usually want comfort after feeding more than more milk. Breast are comforts for them.Babe should be eating every 2-4 hours if not more frequently while clusterfeeding.

Follow bubs lead they will give you very clear signs on when they are ready for their next feed. No need to be on a regimented schedule or volume unless advised due to weight issues