Welcome to the forum. A lot of people have fun with this business, but keep in mind it is work and can be hard work at times.
There isn't a general answer to how long an assignment might take. It varies with the complexity of both the job and the report. Those two components go hand in hand with the pay. One thing to keep in mind as a new shopper, most assignments will take much longer in the beginning. It is normal and as you get used to the requirements and the reports everything will go more quickly.
It will also be up to you how much money is worth your time and your gas. Mystery shopping companies assign fees to jobs based on their needs and what the market will bear. Your travel time and gas are of no concern to them.
Equal rights for others does not mean fewer rights for you. It's not pie.
"I prefer someone who burns the flag and then wraps themselves up in the Constitution over someone who burns the Constitution and then wraps themselves up in the flag." -Molly Ivins
Never try to teach a pig to sing. It's a waste of your time and it really annoys the pig.