In CPython, built-in methods are implemented in C (or some other language, e.g. C++), so it is not possible to get a func_code (that attribute exists only for functions defined using Python).
You can find the source code of time.time here: http://hg.python.org/cpython/file/v2.7.5/Modules/timemodule.c#l126
Other Python implementations may make func_code available on built-in functions. For example, on PyPy:
$ pypy
Python 2.7.1 (7773f8fc4223, Nov 18 2011, 22:15:49)
[PyPy 1.7.0 with GCC 4.0.1] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>> import time
>>>> time.time
<built-in function time>
>>>> time.time.func_code
<builtin-code object at 0x00000001017422e0>
>>>> time.time.func_code.co_consts
('time() -> floating point number\n\n Return the current time in seconds since the Epoch.\n Fractions of a second may be present if the system clock provides them.',)
func_code, so no, you can't.