In the store you may notice some small red banners on some of the packages that show a percentage. This is not a bonus of rubies that you will receive for your purchase but instead an indication of the savings made for purchasing that package of that size.
In the above example the 15,000 ruby package shows a percentage of 20%, this does not mean you will receive 20% extra than what is displayed but instead that purchasing that package will save you 20% in comparison to purchasing the 2,500 ruby package 6 times to receive the same amount of rubies. The store will always show the amount of rubies you will receive for your purchase, even during a Prime Time ruby bonus offer.
In this example the 19,500 ruby package would normally be the 6,500 package but has already had the 200% applied to it, this can be seen by the crossed out 6,500 beneath the total in bold on the top of the package. This of course means you will not receive an additional 200% bonus on top of the purchase as it is already applied in the store. You can also see a timer at the top of the store to let you know how long you have until the offer ends.