Can you share the time that you expected to receive and the time in the e-mail generated by the alert?
What is the difference between them? It is the same difference as the one from your timezone and UTC?
In elasticsearch all date time values are stored as UTC and, if I'm not wrong, currently the alerts will populate the messages using the UTC time, they will not convert it to your timezone as Kibana does.
At least this is the behavior that I have in my alerts, the date time are always in UTC, so an alert received at 07:30 in my timezone, will appear as 10:30, as I'm in UTC-3.
I think your issue is the same as the one in this post.