I don't quite understand your question. Do you want to start a timer after you have received an event? Or do you want to prevent event execution before certain other events have happened?

If it's the latter, you can just use an outer variable to check:

my $seen_event_one;

sub event_one {
   $seen_event_one++;
   # rest of event handler here
}
sub event_two {
   return unless $seen_event_one;
   # rest of event handler here
}
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