I don’t think a primary candidate can announce his VEEP until the convention.
Who said? He can name a VEEP anytime he wants.
They can at anytime.
Sure he can. It’s just not traditionally done, because you usually want to save that as a bargaining chip to secure the nomination, or as a bone to toss out to help heal the wounds caused by primary infighting.
A candidate can name the VP choice anytime but it is not official until approved by the delegates at the convention.
I think they can do it anytime they want.
Mostly they hold out to get $$ support from their party.
I think Cruz did in 2016?