I'd like to set new appointments to default to start of work day for the currently logged-in user in dynamics 2013 (on premises if it matters).
Is there any way to do a query against the user's work hours via JavaScript, or do I need to do this with a plugin as in the SDK example, or is there some other way to accomplish this without custom code?
Yes.
If the work hours are stored in CRM... You can use rest, the sdk.soap.js, JCL or another JavaScript library to query the work hours for the user.
If not stored in CRM but stored elsewhere, you have a few options (plugin, JSONP, etc.)
Lastly, if you can deduce the logic based on the user attributes/roles, you can do this via JavaScript.
Any approach will lead to having JavaScript on the form load setting the default time. Make sure to check the form type.
