The body does a good job of absorbing blood which becomes scabs. However, it doesn't always manage to do it all if there's a lot in one place. The iron oxide from the hemoglobin cells is released when the cells break down and changes to a different oxide (bright red to rusty brown), which is literally rust. This is magnetic and if significant amounts remain, it interferes with any future MRI scans, reducing the detail which can be seen of the prostate around the rusty areas.
So, it's a good idea to get it out if you can, but don't bust a nut over it...
After a few days, it should have gone rusty colour. If you are still seeing bright red blood, that suggests new bleeding and maybe you're overdoing things.
WIth my first TRUS biopsy, on the way out I asked the urologist how long to wait before ejaculating, and he said, "don't wait". Well, I decided to wait until I got home at least😀, and then nearly 24h because I thought it might be painful, which it wasn't. It took 3 weeks to get it all flushed out.
My second biopsy was a template biopsy under general anesthetic. I'd been on Bicalutamide for 10 weeks by then and had very little semen as a consequence, and this meant I couldn't flush out the blood. About 3 months later I had a full body MRI scan (looking for mets). I got to speak with the radiologist who analysed the scan, and one of the questions I asked was that prostate cancer was supposedly hard ot see on MRI, but I had a bright white area in my prostate. Answer was that's not cancer, but an area of iron oxide left from bleeding, and as it's magnetic, it shows very brightly on an MRI scan.