my grandma was named as part of her friend's estate and wants to know how long after probate she will wait to receive her inheritance?

No.  Once your grandma outlived her friend by 120 hours (five days), her share of the estate under the will is hers, and would be payable to her estate if she passes away before it's done.  So, if necessary, the estate could sue the executor if later on he refuses to pay.  And your grandma's medical bills could then be paid from that money, as she intends, by the estate.

Since it sounds like the nephew might be under a mistaken idea about the law (or what he can get away with) in the event of your grandma's death, I'd recommend that, if she passes away before she gets her inheritance, as soon as possible afterward whoever is going to handle grandma's estate goes to the courthouse and gets the paperwork, hires a lawyer, and has the lawyer write to the nephew, to "put him on notice."