Your window to get things started is pretty small.
me·di·o·cre
[mee-dee-oh-ker] adjective
1. of only ordinary or moderate quality; neither good nor bad; barely adequate.
2. not satisfactory; poor; inferior.
In the Navy, we rotate a lot, and end up having to quickly pick up new jobs, only to turn them back over in two years (if we're lucky, sometimes we get yanked faster). The conventional wisdom would be to not rock the boat until you get yourself oriented (normally in 6 months). Then, at that point, you might be able to make some small changes, and maybe keep them in place long enough to turn them over with your relief.
If you do this at every job...you'll likely change nothing for the long term.
The time to implement changes is shortly after you arrive. This will give you a long enough time to see those changes fully implemented, as well as make adjustments should you not have the full answer right away. You only get about a week or two to get oriented, and another two weeks to decide on major changes that need to happen. After that, it's going to take longer and longer to implement change...and it'll have less chance of sticking.
A former 3-star boss of mine attempted to change the way our command was organized in the last 6 months he was in charge. He retired shortly after signing the new structure...and the incoming guy threw it out about a month later. If he had reorganized right away, we would have had two years under the new structure, and if it was indeed better, the next guy would likely have hesitated to change it.
When you get to a new job, spend the extra time learning it inside and out, and make your changes quickly. People expect change with a new boss. After a while, you're no longer the "new" boss, so the expectation of things changing goes away. Soon, you're in a routine. If you built the routine, you have the chance to change how business is done, and leave a positive mark on your organization. If you execute someone else's routine...things will stay the same.
Figure out what you're going to change and do it quickly. Make it your new routine, or else you'll just be a copy of the last guys routine.
