Really interesting idea! The risk-reward of waiting for a clock to get close to 0 was a nice touch.
Controls definitely felt awkward. Arrow keys plus mouse was kinda awkward positioning for hands, might have been nice to be able to use WASD for navigation. And my mouse wheel made it really hard to accurately shift between weapons, and my instinct was always to click on them anyway, which made some levels a lot harder than it felt like they should have been.