I will be available up to 2 pm today, after which I will not be available until 12 am.

Additionally, over the next three days, I will not be free in the afternoons until 12 am.

It's talking about the nucleus of the atom, so it's referring to the protons , which is about 0.8768 fm or 8.768 x 10^-16 m

Ya, but all along I have thought that the diameter of an atom is around 10^-10 or one angstrom.

I mean the proton I thought was also 10^-10.