I am guessing that @bebef1987 took that value from https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/gaia_test.py#L314, from whence much of the code in this base object comes. We made that 30 because of some slowness which was causing tests to fail, and there doesn't seem to be a downside to a higher number as long as the correct methods are used.

+1 for a future enhancement to set this via the command line though.