If you use time, you must consider the twelve and twenty-four hour models over the world. Twelve-hour systems, as used in the United Kingdom or USA, use am and pm to define whether the time is before or after lunch.
You must ensure that time zones are reflected in your application. Which time coding do you need? Local times, like Eastern Standard Time (EST) in New York, Mountain Standard Time (MST) in Colorado, or Pacific Standard Time (PST) in California, USA?
Greenwich Mean Time (GMT) is international time and is the basis for the world time clock. GMT is the preferred time if you exchange data in other countries. This time system is based on the local time in the English city Greenwich (GMT+0). All time differences are given in GMT+x or GMT-x. For example, France, Germany, and the Netherlands show GMT+1, PST is GMT-8, EST is GMT-5, and Japan is GMT+9.
Differences may also occur in summer and winter. Most countries have summer time savings, although Japan and at least one Canadian province do not.
There is another time system, Zulu or UTC. If you need to code time, such as in e-mail or Internet formats, you can check the related RFCs to store time.
Make sure that you store time internally and always use the same time zone in files. When you display a time format, use the correct system settings. The Windows API provides functions to get the appropriate values. In .Net, check the culture name space.
Use GMT time coding, instead of local formats, such as MST and PST. These time formats are not common outside the USA, and an US user probably has no clue as to what CET (Central European Time) means.