When does a JIT compiler perform its translation of a method?

JIT is a service available at CLR (stands for Common Language Runtime).

JIT Compiler performs the translation of the assembly IL code block to Machine interpretable OS native language at the time of execution and on demand only.
That means whenever it will be needed and demanded, just in that time JIT compiler performs its translation. That is why it is called JIT Just-In-Time Compiler.

To be more specific in that execution process, the schematic flow of the translation will be as follows:

1. Assembly Resolver identifies private and shared assembly for execution and passes the request to assembly loader.

2. Assembly Loader loads the assembly into application process as directed by assembly resolver.

3. Type Checker checks for type safely verifying the types used in program with CTS or CLS standards of the CLR.

4. Afterwards if the mandatory security and safety conditions are successfully progressed, then CLR performs the JIT translation for the on demand IL (Intermediate Language) Program to convert the same to machine native language.

5. On completion of the translation by JIT, the managed code is supposed to executed by CLR.