You are free to keep earnings in your Ibotta account as long as you like, especially if you're saving up for something big!
You may allow your earnings stack up until you reach your personal goal and withdraw when the time is right for you. However, when you keep your earnings in your account, the earnings may be subject to account maintenance fees if you discontinue using the app for six consecutive months. For more about account maintenance fees, please check here.
Earnings & Withdrawing Cash