The benders which I use bend one rail at a time. Just curve the rail (can be close, not exact) then slide the rail into the ties. File the end of the rail with bevels so that it doesn't snag on the plastic. Run a candle along the edge and bottom of the rail for lubrication. Should be able to assemble about 6 feet of track in about 15 minutes. It is important that you nip between the ties every third tie or so (for aristocraft and lgb ties) on the OUTSIDE of the curve so that your ties curve easily.
I have used the Train Li railbender which can bend both rails in place on the ties. It is an easier way to go, but is alot more expensive.
If you're spiking your own track, bend the rail first then spike it. One or two plastic ties every foot or so should be sufficient to hold the rail in shape while spiking. I use wood gauge blocks my self. About an hour per foot sounds about right.
Terl