When was Helium?

Answer 1

Helium is a naturally occurring chemical element therefore it can never have been invented but instead it was discovered.

Though the above is true, Helium is the second lightest element in nature, right after Hydrogen, the lightest element. During the first 300,000 years after the Big Bang, ionized gases (plasma) combined together quarks and electrons to create Hydrogen, then eventually Helium, Carbon, Oxygen, and so on.

So by "invent", I took it as you mean when was it first created in nature. It would have been first created when the first protons and electrons got together to mingle with neutrons, whom of which came later on, in huge molecular clouds that then created the first proton-stars.