Is it okay to break off dried old canes on my hydrangea now? Or better to wait until it has bloomed?

The exact answer would depend on which type of Hydrangea you have but for the most part if the can is 'dead' it is safe to clip it back to the point where you see the leaf buds swelling.

I also live in Zone 6-7. I never prune anything until it starts to leaf out. I have discovered that pruning in the fall (like I always did in CA) only leads to die-back from where I pruned. If I leave the plant until it decides where to leaf out, I end up with bigger plants.

So prune back to swelling buds now. Those dead cane tips aren't doing anything but making your plant ugly. If you wait, it will be harder to prune with all the new growth in the way.

Daisy