How much inactive time can elapse before the designer would close out and not save edits?

Interactive Designer itself should not have any session timeout. However, if you are working from Pressero, there is I think a 2 hour session timeout after which your Interactive Designer session could not be added to the cart.

Forms based edoc within Pressero has the same 2 hour session timeout. Forms based edoc in an IFrame (integrated to your own ecommerce system, or testing from Creator) has a 20 minute timeout, I believe. That can be increased if it is causing a problem.