We submitted an article to a SCI journal 2 months ago. Since day 1 the status of article is "Editor Assignment Pending". In the journal introduction they have mentioned that on average 1st review response takes 70 days. As the start of review process usually takes 5-15 days in my area of research; therefore, we sent an email after 30 days and 2nd email after 45 days but there is no response from editor. In second email we requested to withdrawal of article so we may submit it to another journal. Can we submit the article to another journal before hearing the response from editor? Usually in my area of research the articles goes into review process within 5-15 days and it takes 2.5-4 months to get 1st review response.
Today it is very difficult to find reviewers, especially good and timely ones, unless the journal is very prestigious or rewards them highly (eg with editorials).
Having said that, this journal seems to be handled poorly. Thus, I would suggest you to pursue another scholarly venue.
If your email was clear in stating that you were definitely withdrawing the manuscript, then you can submit it wherever you want already.
Be prepared though that they may try to dissuade you stating that the revision process is already quite ahead (which could be true but not necessarily).
The delay in review can vary widely between journals and it does depend upon many factors such as availability, field of specialization, and the procedural overhead of the publisher. However, the delay in response is something that cannot be overlooked, especially if it is as long as 45+ days.
As you have already sent the manuscript withdrawal note to the journal, then it would be ethically acceptable to send the manuscript to a different publisher altogether.
A real life experience from my colleague in multimedia: the paper was submitted to a very reputable publisher. Alas, the number of reviewers for that field is minimal. Adding on to this is the editor's negligence. After two agonising years, the result was given: out of scope.