To enter a date, you should use a slash or a hyphen to separate the parts: 7/16/2009 or 16-July-2009. Excel will recognize this as a date.
If you need to enter a time, type the numbers, a space, and then "a" or "p" — for example, 9:00 p. If you put in just the number, Excel recognizes a time and enters it as AM.
Tip To enter today's date, press CTRL and the semicolon (;) together. To enter the current time, press CTRL and SHIFT and the semicolon all at once.