Not all of your charges will be eligible for Pay Over Time. From what I understand, the charge must be above $100. So anything lower has to be paid in full and cannot be floated.
IMO, it's kind of confusing, and if they're going to make the Gold a revolving product, they need to just go all the way. This charge/revolving hybrid thing is just weird. But, the way it is right now, it's best to just use the Gold card as strictly a charge card.