If I've read this correctly, bleeding can occur up to 14 days after the procedure (although that doesn't mean that it will last that long once it's started):
Quote:
"Removing polyps causes a risk of bleeding, which can occur immediately or up to 14 days after the procedure. This generally stops on its own but very occasionally requires a further colonoscopy or a blood transfusion. There is also a small risk of causing a hole in the bowel wall (perforation). This happens in approximately 1 in every 500 patients who have a polyp snared or 1 in every 100 patients having EMR. This may require treatment through the endoscope, by antibiotics or rarely, by an operation"
Source:
http://www.pat.nhs.uk/downloads/patient-information-leaflets/gastroenterology/803%20Bowel%20polyps.pdf
If the bleeding is severe, accompanied by pain or otherwise giving you cause for concern, I suggest calling 111 for advice.