My recently bought 2004 Chevy Suburban 1500 is throwing P0171 and P0174 codes. Which indicates lean conditions on both banks. I found the MAF had a busted housing, which let in more air than it should. This has been fixed with a new MAF. I also inspected the air intake components up to the throttle body and cleaned the throttle body. I cleared the codes but they returned about a 100 or so miles later. I've read that the engine may take some time to figure out the condition is fixed. Is this true? Or do I still have a true issue going on?
If the codes were truly cleared, you still have an issue.
The fact that they took 100 miles to reappear is a good indication that the codes were cleared correctly, and you still have some sort of lean issue - perhaps so-called "false air" or un-metered air entering the intake.
In my day this was simply called a *vacuum leak". Spraying carb cleaner or venting small amounts of raw propane around all intake and vacuum lines may help isolate the problem. A sudden rise in idle RPM will help locate the leaking component.
While there are a myriad of other causes for P0171/P0174, this seems the most likely given your info and the age of the vehicle. Also inspect the large hoses connected to the MAF, especially the flexible "accordian" sections, as these can have hidden splits and cracks. Which open intermittently due to engine torque movement.
To answer your question, it takes a certain number of specific condition "drive cycles" to complete the so-called "monitor" tests. However, no codes will reappear during this process, unless the condition is still present.