I'm not sure if it's possible to change in the editor. I guess you could hack it in with jQuery, though I found it easier to edit the plugin itself. Note that the 'datetime' type didn't work for some reason (not sure if it's lack of support or what), but the 'date' type did, so I added that.
You can download it here --
Put it in Construct 2\exporters\html5\plugins
Add the updated 'Textbox 2' object to your layout, and change the Type in the properties window to 'date'. I tested it on chrome and android and it seems to work on both.
EDIT: according to this, DateTime only works in Safari --
So i updated the extension to also include the 'time' type - so you can just use 2 separate text boxes (new link above).