It's regrettably not possible to go back to that screen to adjust your goal time.
It's only available at sign-up and is more a guide than an actual prediction of what you'll be able to achieve.
Your target body fat percentage, current weight and body fat percentage and weekly activity levels are what affect your meal plan, rather than the amount of time you plan to follow it for. It wouldn't be healthy or earn sustainable results to cut calories more drastically for faster results.
How much weight can I lose in a week?
As a general guideline, it’s usually considered as healthy and long-term beneficial to lose around 1 pound (0.5 Kg) weekly. Theoretically, this would be caused by consuming 500 calories less daily. Cutting down calories further doesn't necessarily mean you'll reach your goal faster as the metabolism usually slows down.
You can progress faster by working out more per week, completing anywhere from 4-12 training sessions total per week, doing training sessions back to back, and modifying your plan accordingly by updating your weekly exercise levels. Just remember to rest one day in order to prevent injury.