How many days do I have to get an appraisal of my mom's house for her trust?

If you are selling the house in an arms-length transaction (a regular, through-a-realtor kind of sale on the open market) then the sales price is the best indication of value. If you are selling to a family member, or in some other way providing a discounted sale price, then you should get the appraisal as soon as possible (because the value that matters is the value on the date of your mother's death, and the more time that passes the harder it will be for the appraiser to determine that price). Incidentally, you probably should not be trying to settle this estate without the assistance of a lawyer. The requirements are many and varied, and there is no substitute for professional advice.