Well, to write a compelling death scene, you need to build up the emotion. Make the reader care about the character before their demise. Also, describe the details vividly to make it feel real.
Well, to write a great death scene, think about the impact it'll have on the plot. Make it unexpected but also make sense within the story's context. Also, focus on the sensory details to make it feel real to the readers.
It's hard to give an exact time as it depends on the manga's plot development. But typically, Yuta Okkotsu shows up when certain events and character arcs lead to his introduction.
To write a digitalis poisoning death, consider the character's initial exposure, the onset of symptoms like irregular heartbeat and nausea, and the gradual deterioration. Build tension by showing their struggle and the efforts to save them, if any.