do you always need seven cards in your hand magic

[RobboX]

do I always need to have 7 cards in my hand?

like if a card tells me to draw a card and I now have 8 cards in my hand, do I need to immediately choose and discard a card or only at the end of turn?

[Void Elemental]

No. You discard down to 7 during the Cleanup Step of your turn.