How long deals are available in greenmangaming website

How longs a piece of string?

Really depends on the deal; some last for very long times, others last for about a week, and some are flash sales. I would guess that this is a day or two, or perhaps a week long sale. I would check their front page and see if they mention the length of their current sale (might be a daily thing). Since it's probably part of their Saint Patrick's Day sale, it probably ends today or tomorrow.

The number one rule when dealing with a GMG sale, buy it now if you really want it, because the duration of any deal is unpredictable.

In particular, with popular deals they often run out of keys and do NOT restock, so it doesn't matter when you think a sale officially ends, it can easily end long before that.