One question most buyers that have written a purchase agreement are asking these days is what is the offer response time from the sellers. The past few years when buyers were scarce, sellers were responding rather quickly if they got an offer but these days with so many buyers and showings sellers are not so apt to rush into anything. Normally the seller will get the buyers a response in about 24 hrs. Right now if there are a lot of showings they may hold off to see if they can get multiple offers. You can put a response time on your offer, but in that case you need to be ready to say forget that house and move on if the sellers choose not to respond in your time frame.
If you are looking at bank owned properties they often will wait days if not up to a week to see how many offers they can get. Generally at some point they will ask for the highest and best offer and then make a decision.
It may not seem fair to the buyers, but the sellers are in control right now with so many buyers and so few homes for sale. The best plan is to make a good solid first offer, be flexible if there are multiple offers, exercise patience and consult with your Realtor for your best plan of action.