My oven takes just under ten minutes to reach 200, so I typically turn it on and set my phone timer for ten minutes.
I preheat it for most things as I find they cook properly, the times recommended for cooking things are based on a preheated oven. Some things I don't bother preheating but just shove them in and switch the oven on, mainly things like casseroles, oven chips, some roasted veg. I wouldn't preheat to roast a chicken but probably would for some fresh cod.