I did a clear blue ultra early test yesterday afternoon and I'm sure I saw a faint line from about 3mins. Then I came back to it later and they was a thin blue, slightly off centre line which I'm thinking was evap?
Did a digital test later that night and got bfn and took another with fmu this morning and got another bfn. 
My period is fairly irregular and usually on the short side (usually between 24-26days). My bbt app says I ovulated on day 11, but when I look at the chart I think it was more likely day 13. This would make me somewhere between 9-11dpo yesterday.
Trying not to read too much into the possible faint line yesterday, as I got 2 bfn since, one using fmu.
Anyone have any experience with Evaps before 5mins?