There is no definite answer to this question. While some say that getting links too fast can pose a problem, others argue against this. However this won't really matter as far as directory submissions are concerned, since the links you get do not appear all at once. Links can be expected to appear over a period ranging from a week up to 90 days after submissions. The pace at which these links appear would seem normal to the search engines.
Nonetheless, for those who want to play safe, our service allows you the option of 'spreading out' your submissions over a period of a 2-5 weeks, to further delay the rate at which you get your links.