Say the time once, and say it with its zone
There is no automatic conversion of the start time into each visitor's local clock, so the zone label is doing real work. Tom, who presents a monthly finance session to teams in three countries, puts the zone in the page title field's time setting, and the confirmation repeats it in the same words. Nobody has to guess whether 15:00 meant their afternoon or his.
If your audience lives in one zone, a plain time plus the label is still worth it, because forwards happen. Someone sends the confirmation to a colleague in another country, and the only thing that survives the forward is what the mail actually said. Write it the way you would want a stranger to read it.