Is there a Sandbox mode?

Does this game have any sort of Sandbox mode that I’ve just failed to discover somehow? Or a way to significantly increase the amount of time between waves? Don’t get me wrong. I like playing the game the way it is. But some times I wish I could play the game like I used to play Command and Conquer,where I just focus on gathering resources and building up defenses and troops, and then go explore the map, and when I’m ready, instigate a conflict with one ore more of the enemies on the map. I would set it so that the enemies wouldn’t attack me unless I attacked them first. Heck, I wouldn’t mind it if I could just drastically increase the amount of time between waves sometimes. I don’t know. Just a thought. Otherwise, great game! I’m loving it.