Too Late to Harvest Cilantro?

I am having trouble knowing when it is time to harvest Cilantro. We have a small herb garden...and the Cilantro has grow to approximately 18-24 in. and looks like it is flowering.
Did we miss the time to harvest and what can we do now?

The ideal time to harvest is just before the plants bolt or go to flower. This is the stage at which the leaves are the most lush and easiest to gather. However, there is no reason why you cannot continue to harvest leaves after flowering begins. In fact, you can use the young flowers if you get them early before the hard seeds develop.
Repeat sowings through the summer are recommended for a continual supply of fresh cilantro leaves. You can sow every 4 weeks.