Looking at a calender when implantation might happen.

I'm looking at a calculator on the internet of when implantation will likely happen. It shows to put cycle day __ but the only thing is it's always different because I have irregular periods. What am I supposed to put? I just put 35 since it's happen more and I'm not sure if I ovulated or when. I had a little brown bleeding that was not that much then it went to light light spotting now it's gone. I had it for 2/3 days it happened the 8 th. Well I put cycle day length 35 and it shows the 9 th is most likely for it to happen. Hopefully.