Happily I think you're operating in a rather different part of the market, otherwise I would feel unable to give you free advice to help you compete with a paying client!

How long to do this from scratch would depend on the skills and knowledge of the person doing the work. It requires some knowledge of PHP, CSS and especially javascript. My notes show that the changes to incorporate this were relatively small, but there were problems in particular with the javascript supplied by the external service and with how it worked with SSL. I'd allow about a day to install and test for somebody doing it for the first time (less if the service provider has integrated some of the feedback I sent them).