When should I start protecting my fruits from the birds? I've got a plum tree that flowered for the first time...

I've got a plum tree that flowered for the first time this year and I can see that the plums are starting to grow. When should I start protecting them from the birds using a lattice or reflective objects?
Answers:    I would use a net. I would also draw from the net on in attendance BEFORE you see the fruit. If you see fruit..so do the birds. You don't want them getting your fruit before you hold the chance to seize your netting on!!

If you keep a bird feeder on the differing end of your patio...closer to your opposite neighbors courtyard (if you know what I mean) that will keep the birds fvrom wanting to gain at your fruit!!
I know where I live the birds don't chomp through any of my berries until they start turning at least pink. So I assume you have rather time before the fruit start ripening.