Responses to submissions, whether they're submitted by post or by email, varies from publication to publication and publisher to publisher. Some are quite good at it, others less so (if they bother to at all). Some editors appear to deal with submissions in strict date order, whilst others give the impression that they sit down for a couple of days every three months and have a good clear out!
Generally, if the work you've submitted has been commissioned, it will be used quite quickly, because an editor will probably have commissioned it for a specific issue. But if you've submitted something on spec, I would certainly suggest you leave it for several months before you start chasing. When you do chase, be polite. It's usually simplest to ask an editor whether they can confirm that your submission arrived safely in their offices, rather than demanding that they make a decision upon your work right now. (No, is by far the easiest option for the editor.) If they reply that they haven't received your submission then you have the option of enquiring if they'd like to see a duplicate copy, or whether you want to take your chances and rewrite the material for a slightly different market.
Some publications will confirm safe receipt and say that they'll get back to you when they can. If they don't give a time scale, be prepared for a long wait. Some will mention when they hope to respond by. Others will simply return your manuscript, rejected.
Always keep an accurate record of when an item was submitted, and also when you chased. In my experience, being able to list three or four dates of contact attempts over the period of 18 to 24 months shows that at least one side of this business relationship is professional, if not the other! Although, do bear in mind that for the one writer who has submitted something it is much easier to keep track of things than it is for the one editor (with no staff) who receives 200 unsolicited submissions a week, and has just been off work for two weeks because his father-in-law broke a leg whilst cutting the lawn and has needed looking after.
If you are submitting topical material, then editors understand why you are chasing. If they're not interested in your submission, they know that you want the opportunity to offer it elsewhere, so do make this clear when you make your enquiries. Of course, this is another reason for why it's useful to submit well in advance. You want to give the editor plenty of time to consider the material, as well as give yourself enough time to chase, and then rework it for another market!
And the waiting period is another reason why you should crack on and write the next thing. How depressing would it be if you'd written an article, submitted it and then waited for 12 months, only to discover that your work has been rejected. However, if after making this submission you'd written another ten pieces, by the time you'd received this rejection, you may have made a sale with one of your other submissions - and if not, at least you still have the hope of acceptance because you have ten other submissions out there!