Dtyjlui

I had submitted a manuscript to an ESCI journal.
It has been over 1 month since I submitted but the status shows "with editor".

I mailed the editor to check the status of my manuscript. The editor informed me that he had sent the manuscript to some referees but he has not received any reply from the reviewers.
He/She further said that if I want, I may consider submitting my paper elsewhere.

How long should I wait for the reviewers to give a decision whether they will review my manuscript or not?

Also my deadlines for submission are due in 2-3 months, i.e. I need to get my first submission within 2-3 months.

What time can be considered enough to withdraw my submission?

The review process often takes a long time. 2-3 months is typical. I’ve known instances of it taking 9-12 months. You need to be patient. This process is about the same for each journal (well most take a month or so at least. You must consider resubmitting to another journal carefully as you won’t save time by starting over, even if you don’t need to reformat it or write for a different audience (note that you cannot submit the paper to more than one journal at a time).

That it’s still with the editor (hasn’t been rejected) is a good sign. If they believe your manuscript does not have relevance to their journal or sufficient merit, they would have rejected it by now. They will now only do so if the reviewers raise serious concerns, it’s often accepted with revisions if it goes out for review.

The editorial process takes a long time. Many scientific or academic editors perform this role as a part-time job on top of their own academic responsibilities. The most time consuming part of the review process is finding the reviewers. They need to find reviewers with the right expertise who don’t have an existing relationship with the authors who are available to review. It can take a long time to get responses for requests to review.

Once they find reviewers, the review process should be quick. Reviewers are only given a couple of weeks to return their completed review (usually they submit them in this time or a few days late). They should decline to review if they cannot do in this timeframe. Once the reviews have been returned, an editor should give you a decision and the reviews within a few days.

Given that you have a few months before you need to make a decision, it seems best to wait. Reviewing takes time and reviewers are often busy. As you get closer to other deadlines you can contact the editor again if you haven't already heard more and withdraw at that time if you wish.

But there seems to be little reason to panic now.

The average time taken to handle a paper varies by field. In the one I'm most familiar with (physics), the timeline looks like this.

In your case, your paper has gone one month with reviewers invited but none that have accepted. That's not good and it's unlikely any of the reviewers will agree to review the manuscript now. If I were handling your paper, I'd be inviting new reviewers already; however it depends on how active your editor is. If your editor is busy/on holiday/not very active etc, then he or she might decide to wait another month before inviting new reviewers. The fact that the editor responded to your query however is a good sign that they're inviting reviewers already.

So I would wait. I'd probably let the editor keep trying for another 2 months at least. As long as the editor is trying, he or she will eventually find reviewers. If you withdraw and submit elsewhere, the process starts from scratch, so you might have to wait even longer and there's no guarantee the new journal will find reviewers quickly, either.