What is ironic about the Friar's arrival at the tomb? What if he had just been 10 minutes earlier?

Every real tragedy in this story is focused on timing - if he had arrived in time to stop Romeo from taking the poison, the Friar's latest plan would have worked and they could have escaped to Mantua until he could straighten everything out. It is ironic that he tried so hard to make the families quit feuding without any violence, yet they did not stop until the two young people were dead.