You must remember that the Retirement Estimator cannot provide your actual benefit amount until you have applied for benefits. The amount may differ from the estimates provide as you earnings may increase or decrease in the future.
What is the time limit for staying on each page?
There are time limits but you will receive a warning after 25 minutes without doing anything and you will be given the option to extend your time on the page.
Who is eligible to  use the estimator?