It shouldn't be a problem if you wait a month or so. There are some things that they should not need to do but will try to charge you for. First, you need to find out what the 45,000 mile service consists of (it should be in your manual). Second, you should knock out the things you can do on your own yourself. After you chip away at that list, there may not be much else to do other than change the oil and rotate the tires.
Do some of the easy stuff yourself and save a bit of money! You can also take it to a service shop (non-dealer) and probably get the work done much cheaper.