Timer Events - newbie question

I'd like to have a PL/SQL stored procedure on a timed event. Nothing fancy, something like

my_proc {
do stuff
timer (500 seconds)
}

timer {
post event my_proc()
}

Can anyone point me in the right direction to get me started. What I'm particularly not sure of is how to make it so the Procedure calls itself to start off whenever the database is restarted, and the correct way to use a timer with PL/SQL

--
Luch
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