There is no quantity field to specify the number that you wish to purchase. If you buy one, then the offer disappears, so how can you buy 2.

“Premium subscription” is a unique status, you cannot stack multiples of them.

Not the subscription but the offers for fleet and moons. Limit of 2. How can you buy two at one time. The offer disappears after a single purchase.

Do you have a timer like that after buying?

After making a single purchase - Yes, every time. I was attempting to purchase the "Maximum purchase" of 2 sets. I don't see how that can be done.

“2 sets per player” means that only 2 can be bought on the given account ever. The timer is just to “stagger” these two purchases, so fresh accounts wouldn't use both of them instantly.