I have built a date/time control which uses one textbox for the date and one textbox for the time. Both have watermark extenders on them (with css classes making the watermark gray) and when the value of the date textbox is changed I would like to set a value in the time textbox if there is not already one there.  I have the javascript working, however the time ends up being set as a watermark and then when I click into the box the value disappears, if I save the page the value is not returned.

End result, how can I make the textbox or extender know that it isn't a watermark value anymore?

Update:

I found that you have to use the behavior and set_Text.  The next problem I ran into is that this is a user control that may appear on a page multiple times so I dynamically set the Behavior ID of the watermark to "bTime_" + ID on load.