I play a Warp World and reveal a Null profusion and a Price of knowledge, what is my handsize? The gatherer rules for Warp World state that revealed cards enter at the same time, so their time stamps are the same. So my question is which one goes first and what is my hand size then?
Assuming you're casting Warp World on your turn—since it is a sorcery—you get to choose which order the effects apply. If someone else cast the Warp World on their turn or you used something like Quicken to cast it on someone else's turn, the person whose turn it is would get to choose.
613.6j If two or more objects would receive a timestamp simultaneously, such as by entering a zone simultaneously or becoming attached simultaneously, the active player determines their relative timestamp order at that time.
This is an update to the answer.
The controller chooses the timestamp order. If no controller, then the owner chooses. This is done in APNAP order.
Example: All players control 2 creature cards each. Then all creatures are exiled simultaneously. All players in APNAP order would choose the timestamp order for the cards they own put into exile this way.
613.7m: If two or more objects would receive a timestamp simultaneously, such as by entering a zone simultaneously or becoming attached simultaneously, their relative timestamps are determined in APNAP order (see rule 101.4). Objects controlled by the active player (or owned by the active player, if they have no controller) have an earlier relative timestamp in the order of that player's choice, followed by each other player in turn order.