4 hours (does a little dance)
With subsequent babies some things are a lot easier - you know they will not break if you put a vest over their head, and your nappy changes would rival the F1 team. You are not so worried about various illnesses and ailments, and if you have breastfed you are more confident having already done it once.
The hardest thing I found going from 1 to 2 was the emotional stuff - how could I possibly love another child as much, keeping no.1 happy etc. Not so hard going 2-3 as you know you will love the new baby, and you know the other two will cope.
As more come along things get more tricky logistically and you cannot nap the same, but the joy of seeing the siblings interact is (mostly) wonderful. If I were younger, could afford it, and was better at pregnancy and birth, I would have more.
Managing illness becomes harder as each one wants your undivided attention, and juggling the vomit can prove tricky.
Do not be put off having more, kids are the best thing ever.