This guide will let you know how to get the Quick Thinking in Warframe. Go through the guide and follow the step-by-step instructions to get it.
Quick timing can drop from corrupt ancients, spawning in the void and occasionally on fissure missions. But you’re going to be primarily farming for them in the void on the node and which is a survival mission.
The ancients will start to spawn around the 5-6 minute mark, and after that, they continue to spawn regularly, so you shouldn’t have to be in the mission for too long before corrupted ancients start spawning.
Also, the mod does have a fairly low drop chance, so it’s likely going to take you a lot of ancient kills before the mod drops, or if you’re lucky, you can get it on your first run.