Overtime compensation

Based on what you write, this appears to have been time that should have been included in the calculation of wages and overtime: that is, you should have been paid for it (and paid overtime when, including this time, you worked more than 40 hours per week). "Work" time does not mean that an employee is productively working every moment; if the employee is restricted or confined to an area and is waiting to be called into action when a truck comes in, that is work, too--it would not be work if you were allowed to leave or had a lunch break (30 minute, 60 minutes, whatever) during which you could do what you want, go where you want, and be guaranteed to not have to work during it, but that is not the situation you describe.
What you describe seems no different than a floor sales associate in a retail store who cannot leave the store but has to stand by in case customers come in; just as that as that associate has to be paid for all the time he/she is restricted to the store waiting for customers, so should you be paid for time spent restricted to the warehouse, waiting for trucks, even if not actively working each moment.
If your state department of labor is not being responsive, consult with an employment law attorney--the 5 of you could retain a lawyer together, spreading the cost--since you may have a viable legal claim for back wages and overtime (though probably not for more than 2 years worth; generally wage claims are restricted to 2 years of unpaid wages).