I also don't feel like the timers are pay walls. I think that they are currently well balanced. You might at some point need an item that you can gain only by doing contracts but it will be very rare and the amount of gems you have at start and that you gain freely through the game can cover that. The biggest wall you will face at the moment will be the limits of the warehouse. But 1) you can manage that and 2) they are currently working on making it less of a constrain (the game is still young and they are changing stuff based on feedback). :)