I did get my + at 9 dpiui but it was very faint. This was also 12dp trigger so I was worried it was that. It was a true + though and I did check every day until my beta and the line got darker. I did use EPT early prediction.
It definitely doesn't work like this for everyone, some don't get their + til more like 14dpiui.
An early might pick up + pg at 10dpiui. That is when I got a +; however it doesn't mean it will happen for me again at 10 days out this time around. Also if you test too close to the IUI with an HCG trigger shot, the test could pick up the hcg from the shot and not an actual pg.
It depends on when implantation happened. For most women it is around 8dpo or 8dpiui.
Louise is correct is stating it will be more accurate at day 14.
I still remember one woman on here said she tested days 10-12dpo and all were neg. On day 13 it was +.
Good luck!
I would wait until 14DPO, but some tests can pick the HCG (the hormone that the tests pick up) up from around 10DPO. But 14DPO would be more accurate. Hope u get your BFP. How many DPO are u?