In your bid, you should have stated the deadline for a reply. The few times you do not receive an answer within a specified time frame, is when you are dealing with a bank-owned property, or a pre-foreclosure short sale property. It seems these instances take several days, weeks, or even a month to get an answer.
Any time you write an offer, it should have an expiration date for reply as well as an ending date of the contract once accepted. Without that, it is a a VOID contract because it has no end date.
You are free to rescind or withdraw your offer at any time prior to receiving an answer and re-submit it with a deadline, but all must be in writing, due to the Statute of Frauds.
I hope this helps! Also, you may want to consult the advice of an attorney for any legal questions you may have about real estate or contract law.