Welcome to Fluther.
Your question is a bit puzzling to me, because Neosporin doesn’t “slow healing” – at all. So I’m wondering if you mean “how long before it slows bleeding”, and the answer to that is “it won’t”.
The general purpose for Neosporin (and for peroxide, too, for that matter) is to provide a barrier to the entry of infection (and for peroxide, of course, to kill any infectious bacteria that might be present). Neosporin also claims to aid healing by “speeding up” the healing process, but I doubt whether that is strictly true. If you’re still bleeding / oozing, then it’s best to cover the wound to prevent additional abrasion and irritation of the skin, and give it a chance to scab over properly and then complete healing.