CVS accepts a wide range of syntaxes to specify dates. You'll never go wrong if you use ISO 8601 format (that is, the International Standards Organization standard #8601, see also www.saqqara.demon.co.uk/datefmt.htm), which is the format used in the preceding examples. You can also use Internet email dates as described in RFC 822 and RFC 1123 (see www.rfc-editor.org/rfc/). Finally, you can use certain unambiguous English constructs to specify dates relative to the current date.
You will probably never need all of the formats available, but here are some more examples to give you an idea of what CVS accepts:
floss$ cvs update -D "19 Apr 1999" floss$ cvs update -D "19 Apr 1999 20:05" floss$ cvs update -D "19/04/1999" floss$ cvs update -D "3 days ago" floss$ cvs update -D "5 years ago" floss$ cvs update -D "19 Apr 1999 23:59:59 GMT" floss$ cvs update -D "19 Apr"
The double quotes around the dates are there to ensure that the Unix shell treats the date as one argument even if it contains spaces. The quotes will do no harm if the date doesn't contain spaces, so it's probably best to always use them.