Day 1.
Was the midwife that said to as well )in fact she changed ds1's first nappy without even thinking about it and I was pleased not to have to get out of bed to even start to be thinking I ought to be doing that!) - although she did say that it was easiest to use wipes to wipe to start with to get rid of all the meconium/poo and that if you were worried about it you could then just use cotton wool and water for a last splash so to speak, to wash off the wipe stuff.
I did use cotton wool sometimes - when ds1 got nasty nappy rash for example. Also found that rather than using regular cotton wool, I got some very cheap cotton wool pads when they were on offer in boots/superdrug and used them - much easier than actual cotton wool, and didn't leave the fibres around that cotton wool did, which I wanted to avoid due to the nasty nappy rash. I didn't use them that much - 4 years on, I still have a couple of packs left! and nowadays they get used for cleaning injuries (boys forever seem to be scraping themselves) or wiping their eyes when they get sore eyes.
fab mw i had for ds2 told me not to bother putting cream onto his bum at all if there wasn't any soreness - that if you are using disposable nappies these days they are so good at wicking away the wee that cream isn't necessary (i had been told to use sudocreme by one mw to start with for ds1 by a mw, different mw then had a fit and said vaseline if no problems...)
anyhow, ds2 had significantly less nappy rash than ds1 who had a regular smear of vaseline as I'd been told at the time.
If ds2 got a bit sore (usually around teething time) a smidge of metanium cleared it up no problem within a day or so. ds1 had nasty sore rashes that needed special creams from the doctor, took ages to clear up. Cream / no cream used on a regular basis was the only difference between them...
sorry, that got a bit off topic.