I know there is delay in the light to fully turn on. Usually this delay is short, I would say less than a second, anything more than that is not a good sign. It's either faulty or a cheap brand. The humming is also not a good sign, I would request that they send you a new unit... not matter what they say. Also, before you call, make sure that all your wiring is connected properly and to the right connectors, (nice and tight). Make sure if any, the negative wires are grounded properly.
you can try and switch out the ballast, and see how they react. If you get the same issues as before, then you know for sure that you have a bad ballast.
Good luck and let us know what happens.