No max that I am aware of, just 8 business days notice to put in the request. Of course everything is subject to management approval. I know some pilots hop around bases to go on vacation several times a year. You can also start in one base and end in another. We also can use "non-approved" bases on a temporary basis. So if I wanted to end my cycle in Seattle (not a crew base) I could request that. Not sure the limits of the temporary basis for non approved bases and I'm guessing they would not approve Alaska or Hawaii unless you could make a very good case on equivalent airline costs. A few minor rules apply, but nothing worth noting here.