Most Inspections take between 2 to 3 hours.
The things that affect the time will be inspector experience along with size, age, and condition. A good inspector will invite you to attend, but will not allow themselves to be distracted by conversation. You should follow them and observe if you want, but they’re there with a single purpose – to make sure you know what you’re buying and have no unwelcome surprises after you move in.
Conversations can happen in the beginning and the end, but in the middle you should let them earn their fee.