When can trades happen?

[WeMadeIt17]

I know we are still about 11 days till the draft but I was wondering can a trade be agreed apon before the finals are over? Or is it that it can only picks that can be swapped? Or does everything have to happen after the finals? I ask because I thought I remeber awhile back the knicks and somebody making a deal before the finals ended but could be wrong just wanted to know. I am so excited for the draft to see what Danny does so I am always that guy waiting for something to happen!