How long does it take to pass from renal failure once they’ve reached a comatose state?

Like the title says.

My grandpa is in hospice and are letting him pass naturally as he is 89, and his kidneys have stopped working. He’s had heart disease for several years too, and we’ve all voted against dialysis because the likelihood of him living through that is slim. Which I understand, because he is 89.

We’ve been visiting him and they explained he has slipped into a comatose state. Sometimes he’ll open his eyes and appear to respond to us. He’s been in this state for about 1.5 days now.

I’m just wondering, how much longer he has? They said a couple days. I just want him to be comfortable. I’m heartbroken because my grandparents practically raised me too. I have a huge close family, and I’m so happy we’re all here.

I just hope in the state he’s in he’s not hurting, and that he can hear us?

I just need some reassurance. Thank you so much.