Iceland in summer is a long daylight story. June through August gives you close to 20 hours of sun, open highland roads, puffin colonies along the south coast, and the kind of hiking weather where you forget what a raincoat is. February and March are the opposite mood: short days, frozen waterfalls, and the northern lights bending over the lava fields outside Reykjavík. Both windows work. They just deliver a very different trip, so pick the one that matches what you actually want to come home with.
For one US traveler, a reasonable Iceland trip — a budget flight, a week of guesthouses, a rental car, food, and a couple of paid attractions — lands around $560. Most people do not have that sitting in cash. The smart move is to keep that money invested or in your emergency fund, put the trip on a card that gives you a long runway, and pay it off in steady monthly bites.
The 0% intro APR is a deadline, not a discount. As long as the $560 is gone before month 15, you pay no interest. If a balance is still sitting on the card when that window closes, the card's regular APR kicks in on the remaining amount, and it adds up fast. Treat the 15-month mark like a real due date, not a suggestion.