Online Help (F1):A backup copy of your project is automatically saved every five minutes.
Read more in Help > Index: Automatic Project Saving
You should also read Help > Index: Saving Projects
If you are desperate to change it, you can load in the 'internal preferences'. There is a setting titled 'MSautosaveInternal'. By default, it is set at 300 000 ms. That is 5 mins. I would imagine that you can change it as desired (and at your own risk).