Eh, you're at 20 weeks, that's usually the perfect time untuk buat detailed scan, actually! Most of us do it around 19-21 weeks, so you're spot on with timing. Normally boleh book dengan OB kamu or the hospital, and it takes around 30-45 minutes depending on how cooperate baby lah. Better go soon while you're still in that sweet window, and the baby position usually clearer at this stage.