5 DPO is about the right time for bleeding if implantation has occured. Some women will experience implantation around day 3...Others as late as Day 10 (After ovulation) so it could well be implantation bleeding.
However, like you say, its quite possible to have some spotting around the time of ovulation, especially if you are prone to long cycles.
I will have everything crossed for you that its implantation spotting!