Spend more time than allocated on complex cases, then run late and short on others. More typical of specialists, but GPs do it too. Beyond that, incrementally, 1 appointment/billing code and a new test/intervention at a time. Until the patient gets better, worse or gives up.

Are you in US? Is double consult something insurance/government pays for twice for you? Or are you are talking about a different billing code? Or self-pay?

Australia. We have different billing codes for different length of time and different complexity of concern/procedure. We book double/triple/etc. appointments when necessary.

Doctors still often go over time.

Interesting. In US there are also different billing codes like that. But it's not something a patient has input on. However, it's safe to expect a provider to chose the maximum code that can be reimbursed at any given time by default.

So given that, a patient is likely getting the most expensive product a given doctor will deliver already. To get a better product simple options are specialists (much higher reimbursements, selection bias for more complex cases) and specialists at major teaching hospitals (even more of the above).

There are effective ways for a patient to hack the system by doing lots of work themselves (e.g. by maintaining his own clinical summary) but they are beyond what most patients will do.

Patients don't really have anything to do with choosing item numbers. They just may request a longer appointment or a specific procedure or test.