What is the event time of an element produced in a timer?

[Marco Villalobos]

If an event time timer is registered to fire exactly every 15 minutes,
starting from exactly at the top of the hour (exactly 00:00, 00:15, 00:30,
00:45 for example), and within that timer it produces an element in the
stream, what event time will that element have, and what window will it
belong to if I am using a 15 minute tumbling event time window?