Hospice will be starting on Monday, how long is the ending process?

Your profile says Mom has a Dementia. Is that the only health problem she has? Usually Dementia is not a main criteria for hospice. Is Mom showing signs of transitioning? This means she is in the dying process. If so, it could be a few weeks, it could be months depending on her decline.

My mothers decline was she would not get out of bed. Then she could not swallow and that was when Hospice was called in. She passed 6 days later. From beginning to end it was 2 weeks. Unless Mom for some reason improves, Hospice will be there till she passes.

At this point, the Hospice Nurse will be your go to person with questions. She will come every 2 or 3 days during the week but should be available by phone 24/7.

There's no answer for that. One poster here had a husband on hospice for 22 months. My mom was on it for eight months and didn't eat anything except Boost milkshakes the entire time. Others make it only a day or two because the family waited until their breaking point before calling in hospice.

Only God knows the answer to that question. My husband was under hospice care for the last 22 months of his life and hospice told me 3 different times that they thought he was dying, yet he continued to live, until his death in 2020.
So just enjoy whatever time you have left with your loved one and make sure that you leave nothing left unsaid.

How long is the ending process? Depends greatly on your mother's current condition. If she is very near her end of life and no longer eating and drinking, it could take days or weeks till she passes.

How is your mother right now?

That depends on a lot of factors.

Is mom on any life-saving medications or treatments that will be stopped?

If not, she could be on Hospice for a long time. Hospice doesn't hasten death.