I submitted a paper to one of Elsevier journals. It got major revision and the submission time given to me was two months. Now the time is very near (10 days) and I think I cannot complete all changes to be incorporated. I asked for extension in due date of submission through editorial system using my login. Even after 4 days, there is no response. I am confused what should I do? Is the deadline really hard and if I submit after a week or so, it will be rejected?
Counting the days, you asked for an extension on 24.12. Not everyone has to be around during the holidays so next time ask maybe a little sooner.
It may depend on the field and journal, but this summer I asked for an extension and I got it. Also considering how certain deadlines are handled around the academia (like 3 months taking the referee to review a revision of the paper just to say its OK), you are probably going to be just fine.
Edit: I just remembered that some time before Christmas I was sent a proof to answer the questions from Journal of Mathematical Physics with a deadline of 48 hours. I guess it took maybe even more than 3 days to send it back and nobody did complain.