As of 04/09/2015 the only answer is "SOON"
no release date set by verizon or Microsoft.
I wouldn't be surprised if Verizon was waiting for Windows 10 phones. Recall the update fiasco for the Lumia Icon. The Cyan update was supposed to be "coming soon" but Verizon chose to wait for the Denim update instead and never bothered to inform customers of this update delay. It was frustrating and ultimately lead to my selling my Lumia Icon. The moral of the story is that Verizon tends to move slowly (think glacial speed) with respect to WP/Windows. There is always the chance that the Lumia 735 won't happen at all and than Big Red will wait for Windows 10 phones.