Thanks for the feedback. Yes, originally there was a visual indicator in form of a text but due to how little screen space there can be for text in a 64x64 game I had to cut it and due to time constraints never added back any visual feedback. Roughly the game is balanced so that once you reach red gems with level 3 drill you are almost out of time. I guess as a developer I playtested the game so much that I can "feel" how much time I have left without audio cues. But a player wouldn't know that so there's certainly room for improvement there.
True, the drilling noise can get jarring after a while. For this jam I realized how much I rely on pre-existing assets and one of the lessons learned is to learn some basic audio editing tools and learn to make my own sounds.