There is no limit on how many times you can discard orders. I've done it many, many times when I don't have enough of the items to make the order or the items required come from a building I haven't purchased yet. I noticed that when a new building is about to be available at the next level, the items for that building start appearing in the orders and continue when you have reached that level, even if you haven't purchased the building.
Tip: If you know you don't have the items to fulfill the order and you can't create/finish them with your buildings in about 10-15 minutes, discard the order, and wait for the new one to appear. Don't waste gems speeding up the order refresh unless you have the patience of a toddler and lots of money to burn
. The refresh doesn't take that long. There have been several times I've had to clear every single order showing because it would take too long to create the items.
That said, once you are ready to take a break from the game, if there are orders that require time to create the items, look at the things needed and make sure that you have them being made in your buildings so they are ready when you return to the game.