technician here you shouldnt have to wait more than the time it takes you to turn off the car and walk around to the hood (for oil, coolant is under pressure when hot) obviously checking on sloped ground might throw off the reading a tiny bit but oil level doesnt have to be a precise thing. the "safe range" is usually a whole quart of variance tbh just taking the time to check it puts you leagues ahead of most people (braindead city women especially). as long as its got oil and you change it regularly, the oil level would have to get lower than would show on the stick to start causing damage