Hey, my girlfriend is scheduled 20 hours tomorrow and I was wondering, is this legal in Missouri? Does anyone know?

Depends on the contract/job, I think.

Are you asking because you are concerned for her well being or because she is complaining to you about it and looking for a way to get out of the shift?

depends entirely on the gig and the state laws of that gig

I work 50 consecutive hour shifts in cali legally

I googled 'how many hours can you work in a day in missouri'

and it was literally the first fucking link: https://labor.mo.gov/DLS/General/overtime

Work Hours
There is no minimum or maximum number of hours an employee may be scheduled or asked to work. This is in accordance with the Fair Labor Standards Act. Missouri labor laws also require most employers to pay or compensate their employees for the number of actual hours worked.

Travel Time
Generally, time spent commuting from home to the workplace is not work time. But time spent traveling during normal work hours as part of the job is considered work time and employees are entitled to be paid for this travel time. Such travel time will be taken into account as work time in determining whether employees have been paid the minimum wage.

Overtime Pay
Employers must pay at least one and one-half times the employee’s regular rate of pay once overtime pay is in effect. Overtime pay begins once an employee works more than 40 hours in a work week rather than more than 8 hours in a work day. State and federal law does not allow employees to voluntarily waive their rights to overtime pay and accept straight time instead. Any employer that asks an employee to do so violates the law and employees should​ file a wage complaint.

I work in Missouri.
Not so bad

GJ! And it was nice of you post it in for him

Glad we have laws to prevent that shit here

why would you ask questions like this on jsp instead of google

This!