You can start playing immediately after purchase
The key thing to build around is the other than your hand line, so cards with foretell (Behold the Multiverse, Delayed Blast Fireball) and flashback (Think Twice, Galvanic Iteration) are excellent
This creature gets +1/+1 as long as an opponent controls an Island
This is important because if you were to choose the targets for spells when you suspended them, those creatures/players/spells may not be legal targets X turns later when the spell is cast and it would just fizzle
This means that if your opponent has evolved Charmander into Charizard using Rare Candy, you'll send the Charizard card back to their hand while defeating Charmander with the 100 damage from the attack
Its one thing for a Callous Dismissal or Spark Harvest to undo your hard work assembling a zombie army, but its another for a Pious Interdiction to also shut off all future progress as well