If something happens by a particular time, it happens at or before that time.
"By eight o'clock he had arrived at my hotel."
It means at 8 o'clock or before 8 o'clock.
"by Friday" means on Friday or before it.
" no later than the beginning of Friday" refers to something happening before Friday and at the latest on the beginning of Friday, in the morning.
"no later than the end of Friday" refers to something happening before Friday, at the beginning of Friday or at the latest at the end of Friday ,at night.