The 4-hour wait time is for worst case cold and contaminated water. In the US you probably never have to wait that long.
Normally a 15-20 min wait time is sufficient. The different packagers of the tablets use different marketing strategies, although they are selling the identical item. Those less infiltrated by lawyers recommend the shorter wait times. I recall one of them even has a table listing different wait times for different water conditions (temperature, contaminant, cloudiness, etc).
I use tablets all the time and never wait more than 20 mins for relatively clear water.
Actually all the recommendations come from an EPA study you can find on the web. There you'll find complete information on wait time versus log reduction of various contaminants, temperature, cloudiness, and a bunch of other factors.