If the employer calls it an all-hands TGIF meeting, is it implying that the meeting is mandatory, or that everyone can attend, but doesn't have to?
Typically, an "all hands" meeting implies that all employees are expected to attend.
Exceptions for this may include an employee being on previously-approved time off, illness, family emergency, or having required coverage of a service (customer service reps having to man phones, front desk receptionist, etc.).
But if you're at work and your being absent from your workstation will not cause a business-critical failure of some sort, you should probably attend at least briefly.