An LSA management agency should monitor your account regularly and make optimizations based on actual performance data, rather than making changes on a fixed schedule. At a minimum, the agency should review lead volume, lead quality, budget, service areas, and account issues every week.
Larger or more competitive accounts may need more frequent monitoring, especially when lead volume or costs change quickly. Major changes should be made carefully, since constantly changing the account can make it harder to tell what is actually working.
A good agency should also give you regular updates on what it changed, why it changed it, and how those changes affected your leads and sales.