Yup, I live near wgtn and find that with big stains I often have to leave them out a day or two to get them completely bleached. I think it's the uv rays that bleach it so the stains do go even if it's not sunny, just takes a bit longer.
Do you have pocket nappies or AIOs? If it's pockets, I'd recommend buying a few extra inserts so you have a few extras to use if you're keeping the stained ones out longer. I find the stains disappear quicker on the outer pocket part but the insert stains take a bit extra. Cheaper than buying extra nappies