It takes much less time and effort to maintain a fitness level than it took to gain it in the first place. The amount you need to do to maintain depends on how often and how demanding theses hikes are and how long you are trying to extend your hiking seaons. If a hike takes a lot out of you then you will need more recovery time before going back to some training. If you have a break of 2-3 weeks between hikes you could have a mini training block to help extend your base fitness for the full hiking season. So, there is no easy answer to this question.
Scott