A planeswalker can activate its ability during its controller's main phase when they have priority.
Yes, you can activate a planeswalker ability during your opponent's turn if the ability can be activated at instant speed.
No, you cannot activate planeswalker abilities at instant speed during your opponent's turn.
Planeswalker abilities cannot be activated on the first turn of a game because they require loyalty counters, which are only added during the controller's upkeep step.
A Planeswalker can only use one ability per turn, and only on your own turns. Planeswalkers do not suffer from summoning sickness though, so may use an ability on the turn they are played.
Planeswalker abilities are activated by the player controlling the planeswalker during their turn, while instants can be played at any time, even during an opponent's turn. Additionally, planeswalker abilities can only be used once per turn, while instants can be played multiple times.
In Magic: The Gathering, planeswalkers have loyalty abilities that can be activated by adding or removing loyalty counters. Players can only activate one loyalty ability per turn, and the planeswalker can be attacked by creatures. If a planeswalker's loyalty reaches zero, it is put into the graveyard.
No. It is an Ignition Effect, meaning you may only activate Snipe Hunter's effect during your turn.
As a trap card, you cannot activate it on the turn you Set it. However you can activate it in any turn after that, including your own, if you wish.
Yes, in Magic: The Gathering, you can activate creature abilities on your opponent's turn if the ability can be activated at instant speed.
You can only activate a Quickplay Spell card from your hand in your own turn. If you want to activate it in the opponent's turn, you must Set it during your own turn.
Yes, as long as it's your own turn. If you want to activate them in the opponent's turn, you need to have Set them on the field during your own.
Since DD Sprite can only be summoned during your own turn, its trigger will activate in the opponent's Standby Phase.