Maximum attainable delay with Micro controller
It is not specified because any normal micro-controller can by means of software create an essentially unlimited delay - ie, of a far longer time than there's any reason to expect the circuit to still be operational or anyone to care about the result.  

Essentially, you find some means of generating a short delay, such as having the processor execute a few instructions, or using a hardware timer, and then you use a counter to do that however many times is necessary to make up the period of time delay you desire.

Each byte of available register or ram storage for the count value would increase your available delay by a factor of 256.  With as little as 64 bytes of RAM (most micros have several times that), you'd be able to create delays where the age of the earth pales by comparison.