I see that timezones is a feature request but is ther any variabl tha can be used in an alert email to add the timezone to the date time
You could add an advanced property to each node called something like "timezone". Set this for each node with whatever you like as the timezone identifier (you could use something like GMT + - minus whatever). Keep your NPM on GMT. Then in your alerts use the variable ${timezone} in the message. This would enable every alert to display your timezone info for each node alerted on. It woud even be possible to take the timezone variable and use it to do the math against GMT and show the derived value.
Also here's some of the built in Time Variables to help you:
