I have the exact same problem. I intended to buy gems to use for items on sale in the gem store 2 days ago, but I chose to buy the $100 expansion since the cost would be the same for 4000 gems and the basic expansion if I purchased them separately. AFTER I made the purchase, the message about having to wait up to 72hrs for my gems came up.
I don’t mind that there is a 72hr wait, I understand their reasoning for it, but they should have made that info very obvious BEFORE I made the purchase. The expansion and the gems are the only things I actually cared about and I would have purchased them separately if I had known about the wait.
Now I am forced to buy additional gems on top of the ones I have already paid for or miss the sales I bought the gems for in the first place. It’s reasonable to be a little annoyed.