It would take you all day at the least. That is a very slow section. It would be better to camp overnight and split into two days. Especailly if you are fishing or just floating along. If you are pushing it and rowing the whole time you might be able to make it from Salida to pinnacle.
If it is windy that could be the longest day of your life. I agree that an overnight would be good for that stretch at this level. Its about 40 river miles at a low flow, I think you would be constantly rowing a minimum of 8+ hoursThere is easy pay camping at Valley Bridge that would split it in half.
I think from Lone pine down to Pinnacle would be the better of the two runs if you had to do them. There are a few more rapids on that section. If you really wanted some rapids you should do from Pinnacle down to Parkdale that is the milk run for the companies. If you are looking for an easy section with hardly any rapids the section from Salida on down would be the one you want. Depends on what you are looking for and how long you want to be on the river.