Instance time and pod time are two different concepts that can affect datetimes in Marketo. The pod time is not something you can change, but you can work around it by accurate application of Velocity scripting (email script tokens). Velocity is also the only way to get the AM and PM added to the output.
If you search my posts on the Community for "velocity locale," you'll get insight into the ways to manipulate and reformat stored dates and datetimes in emails. Tagged posts at http://blog.teknkl.com/tag/velocity are also recommended.
In addition to Sandy's recommendation above, I'd recommend confirming whatever is stamping your value on the lead for Appointment Date Time. It sounds like that is what is marking the NY + 6 hours time.