Electronic – Maximum attainable delay with Micro controller

Yes, this is possible in a number of ways. What you need is a disassembler that supports the target microcontroller you have.

The simplest way to do this for a PIC is to use MPLAB. I use the older version (v8.90) for this but there is most probably a way to do it in MPLABX also. Load the software then choose File->Import and open your .hex file. After this you can use View->Program Memory to see the assembler.

This might not bear much representation to the original code if it was written in a compiled language (for example C), but it will be an accurate representation of the exact instructions the microcontroller would run.

There are other free pieces of software that can do this. You can also find paid offerings like IDA Pro, which become very useful when starting to disassemble bigger portions of code.

By hardware delays I meant 'Timers'.

The advantage of using timers to realize a delay is that they provide a way to allow async counting. Using a "Software delay" you force the controller to put all its resources into processing some kind of loop (incrementing a variable until a given value) and thus blocking the rest of the code execution path.

If hardware delay is so good then why is Software delays needed?

A software delay is easier to implement and may be sufficient if its just a very short delay which is not significantly interrupting any other task in the main sequential code processing path. Furthermore, the timers may be in use for some other hardware related tasks like PWM generation and may not be "free" to be configured according to your delay requirements.

Another use case would be some initial delay that is required before the main loop is running. There would be no need to use a hardware delay in that case.

One last thing that comes to mind is that a software delay doesn't require interrupts to be globally enabled, while its a requirement for timer based delays (at least for the common use case).