I've never understood the difference between "further" and "farther" and a quick google search tells me there is not much of one when the words are used as adverbs. Some sites say "farther" is preferred.
I believe the word is being used as an adverb in the sentence "We might go a little bit farther." This is what Bruce and I were talking about today in a phone conversation.
My work schedule is very busy early in September, the result being a little extra time off later that month or early October. So maybe an extra day or two on the water. Our goal is to reach Ocean City, Maryland. If, and that is a big if, the weather in tides cooperate we could possible make Chincoteague or Wachapreague. With an extra day, and - again - cooperating weather and tides, we could possibly go a little bit farther and make Oyster or even round the bottom of the peninsula and reach Cape Charles. We've still got to check on flight schedules and a few other things.
At the very minimum, having the extra day or two gives us more weather days.