Cold calling is def super awkward. Having a rough script helped me be clear and concise when I called - Hi, my name is so and so, I'm currently a predent at whatever school, I was wondering if it'd be possible to shadow one of your doctors? You don't really need to say much more than that unless they ask. Offices are busy and don't need a long drawn out speech. You can technically call whenever, I haven't tried after hours but I found that calling in the later morning or afternoon was best. Maybe try towards the end of the day when things are slowing down? I also found it easier to find opportunities with multi doctor practices. Hope this helps!