If multiple effects modify a player's hand size, apply them in timestamp order. For example, if you put Winter onto the battlefield and then your opponent plays Reliquary Tower (a land with "You have no maximum hand size"), that opponent would have no maximum hand size no matter when you started having delirium. However, if the permanents entered in the opposite order, that opponent's maximum hand size would be seven minus the number of card types among cards in your graveyard if you had delirium. At any time you didn't have delirium, they would have no maximum hand size.

A player's maximum hand size is checked only during the cleanup step of their turn. At other times, they may have more cards in hand than their maximum hand size.