How long would it take for 100 people to evacuate a small room when the fire alarm rings?
That would depend on the number of exits, the width of each exit, how clear the path is to the exit, and the people involved. I'm sure OSHA has guideline figures on such things.
Yes a small busines can benefit from a wireless alarm system. Whether big or small, if you can afford it better get an alarm protection. It will give you some peace of mind and extra protection for your business. If it has a wirelss camera secutiry system you can monitor your business from anywhere by accessing it on the internet.