Many spells and abilities generate continuous effects that apply to permanents in the battlefield. Effects like these only apply to those permanents that were in play when the spell or ability resolved and the continuous effect was generated.

For example, Turn the Tide only affects those creatures controlled by when Turn the Tide resolves. If a creature were to enter the battlefield after you you were to play and resolve Turn the Tide, then that new creature will not get -2/-0.

Keep in mind that this does not apply to continuous effects that either affect the rules of the game or a player. Gideon Jura‘s first planeswalker ability affects the rules of the game and does not affect the characteristics of these creatures. Because of this, creatures that enter play after Gideon Jura’s ability has resolved will attack Gideon if able.