Usually second half, mostly third trimester as the bump and weight increase. Some get early, some late, some none. It's a lot about genes too, my mom had them so I did.
They typically show as the skin stretches more, around mid to late pregnancy. I oiled daily with coconut/almond oil from early on. It may not fully prevent but kept my skin less dry and itchy.
Mine started showing around the 6th-7th month when belly grew fast. I felt a little upset at first honestly but then I made peace, they're a part of the journey.
Don't worry too much about timing, they often come in the later months. Keep skin moisturised and hydrated, and remember they fade a lot after delivery anyway.
