I don't believe Mica is a coward to repeatedly run away. Her character wants to save the lives of others even when she can't. Of course she wants to save Do Ha's life over her own. I also wondered why cant they just share their time.  He feels like he will perish without her and she is going to perish one way or another. They should just come to an agreement to exit life together. They could easily share time by simple calculations. They would only need to calculate how much time that she consumes from him per day, and subtract from the amount of time that he would give her so that they have equal amount of time together. They would need to readjust the shared time when her time stop, increase, or decrease. 

Not to sound obsessive as crazy Bae or anything about the math, but I have thought about watching the drama again to see if the time that Mica consume can be determined throughout the drama. 

Is anyone eles interested in calculating this?  🤓

Also could the concept of spending time, sharing time, taking up someone's time or givng time simply just be a metaphor and the writers are playing with the audiences preception of time? 

I would love to hear other thoughts on this and other theories of the drama.