E.S.
I had IB w/ 2 of my pregnancies. One I lost, one I kept. It was like the start of a period for me, not really bright red blood, only present when I wiped. When I didn't start my actual period a few hours after I first saw it, I knew I was pregnant.
If my memory serves correct, it lasted no more than 24 hours.
But of course, everyone is different. ;)
HTH! GL!!!