> I say this because bipolar disorder is a protected condition under the ADA, which allows for work modification.

Allows for but doesn't require. Workplace accommodations for any disability have to be reasonable and it's generally up to the business to decide what's reasonable. You can sue but most businesses would not find it difficult explain why it's important for employees to be working roughly equivalent hours and in the office if that's what everyone is doing.

BTW, deciding your own hours with little direction about how you complete tasks sounds more like a contractor than an employee.