Simply put, warrants never expire. However, suppose the criminal statute of limitations (SOL) has expired. In that case, you might be able to get the case dismissed for passing the time limitations. In California, the SOL for misdemeanors is generally one year from the time of the offense.
A stock warrant can cover any number of shares and often will have expiration dates far longer than stock options. Expiration dates of five, 10 or even 15 years are not uncommon for warrants.
The two main rules to account for stock warrants are that the issuer must recognize the fair value of the equity instruments issued or the fair value of the consideration received, whichever can be more reliably measured; and recognize the asset or expense related to the provided goods or services at the same time.
The easiest way to exercise a warrant is through your broker. When a warrant is exercised, the company issues new shares, increasing the total number of shares outstanding, which has a dilutive effect. Warrants can be bought and sold on the secondary market up until expiry.