Problem passing datetime variable with colon via url

Hi,
My seemingly simple requirement is to send a datetime variable (amongst other variables) which includes a colon (e.g. 2013-07-01T13:30) to a partner’s website via an URL for an availability query. This I need to do via a form and the GET method. However, when the form is submitted, everything is OK in the destination URL EXCEPT the colon which is changed to %3A (in example above, 2013-07-01T13%3A30), and the availability query subsequently fails with an invalid datetime error. How can I get around this?

Hope someone can help as much googling hasn’t come up with a solution.

cheers

The problem is on the other end. The partner’s web site is not decoding URL Encoding.