Use the littleworkers library to fetch many gitrepos at once.

gitFetchAll.py

#! /usr/bin/env python

from littleworkers import Pool

# Define your commands.
commands = [
    "cd repo1; git fetch",
    "cd repo2; git fetch",
    "cd repo3; git fetch",
    "cd repo4; git fetch",
]

#fetch em all at once
lil = Pool(workers=len(commands))

# Run!
lil.run(commands)