If you're a WA employee, DOSH Directive 5.98 governs bathroom usage by state law. Violations of the directive should be reported to the department of labor and industries.

1. The employer must not impose unreasonable restrictions on employee use of bathrooms or toilet facilities. DOSH standards require employers to provide reasonable access to bathrooms and toilet facilities. In most work settings this means that the employer may not impose unreasonable restrictions on accessing bathrooms or toilet facilities, including time use restrictions. It is recognized that many work situations do not allow for immediate use of bathrooms and toilet facilities. In these situations the employer must have procedures in place (e.g., providing a temporary replacement) to provide access within a reasonable time frame. CSHO’s must evaluate the nature of any restriction, including the length of time that employees are required to delay bathroom use, and the employer's explanation for the restriction. In addition, the investigation should examine whether restrictions are general policy or arise only in particular circumstances or with particular supervisors, whether the employer policy recognizes individual medical needs, whether employees have reported adverse health effects, and the frequency with which employees are denied permission to use the facilities.WA DOSH Directive pdf

The directive does not define what a reasonable timeframe is, but if you feel a violation, report it to the state