By rule, since you didn't invoke 3-5-10 by calling an officials time out, the player wasn't sent off for visible blood, but simply substituted and may return after a timeout. If you're sending him off, you need to stop the clock to make it apparent to both teams that the player is being sent off.
Now, if he tries to come back in while still visibly bleeding/covered in blood, you can send him back off and invoke 3-5-10 this time.