When you put your home on the market, the expectation is that you will have an acceptable offer and be in escrow, by the end of 30 days.  Every 30 days, you need to evaluate why you haven't received an offer, OR why the offer you received didn't make it into, or through the end of, escrow to closing.

The first 10 days is the most significant timeframe to get the property "positioned to sell".  If you started at the right price.  If you staged the home and cleaned it to be the best it can be.  If you have 10 to 15 good quality photos showing on all of the public sites.  If you didn't start showings until the property was on good showing condition.  If you have done all of these things, you should have an offer within 30 days and be closed within 60 days.

At the end of 30 days you need to evaluate why you do not have an offer, and make changes.  Sometimes you know these things immediately and change a few things in the first 10 days.  If you did make changes in the first 10 days, then you need to wait 30 days from the change.  If at the end of 30 days you make additional changes, then you need to wait 30 days from then.  At 60 days you need to take a harder look and at 90 days, if you have refused to make changes since day one, you really need to decide whether of not you want to sell the house.  If you have had no offers in 90 days, no matter what Zillow says about the value of the property, you need to make some changes if you are going to be successful in selling your property.

Generally there is no need whatsoever to be alarmed until you get to 60 days.  If you have had lots of showings and no offers, there is likely something wrong AT the property.  If you are getting no showings, then there is likely something wrong with the price.  If people are making appointments and then not showing up, then you have an exterior problem that is not readily apparent when viewing the property on the internet, but is obvious once they get within range of your front door causing them not to come inside.

Don't be the seller who says, "Can you go back to that buyer who offered us $790,000 three weeks ago, and tell them we wish we had that offer back again!"  Take the time now to think about how you will respond, if and when an offer at less than asking price comes in.