When was Bill turned into a Cyberman?

Question

In Season 10, Episode 11 World Enough and Time Bill is shoot and taken away and later wakes up to find she's been fitted with a replacement heart. When the Doctor ends up reaching the floor Bill was taken to he encounters a Cyberman who says it was Bill.

In the next episode The Doctor Falls we see Bill like normal but it's revealed that she hasn't been reverted and is still a Cyberman and remains so for most of the episode despite times where we see Bill in her human form.

Since we see Bill as a human in episode 11 when talking to Razor, do we know if at any time she was talking to Razor, if Bill had been upgraded to a Cyberman and it was just her thinking she was human (like what happens at the start of Episode 12 before The Doctor shows her reflection)? If so do we know when the upgrade occurred?

Answer 1

She was Bill until about two hours before the doctor arrived on that floor, if the Master is to be believed.

He says to the doctor, "Ten years you spent up there, chatting," referring to the length of time that elapsed on the lower deck of the ship. "You missed her by two hours."

Answer 2

We see Bill going in for her conversion, two scenes (maybe a scene-and-a-half, depending on how you count) before the Doctor meets cyber-Bill; the dialogue of that scene pretty clearly indicates that Bill has been human the whole time, cybernetic heart notwithstanding:

Surgeon: I'm afraid, Miss Potts, it's your turn.

[...]

Bill: Don't you touch me. Don't you lay a finger on me

Surgeon: This unit of yours won't last forever, you know. You need the full upgrade.

Bill: You're not going to turn me into one of those things.

[...]

Surgeon: [picks up what is clearly one half of a Cyberman headpiece] This won't stop you feeling pain, but it will stop you caring about it. It fits over your head.

^{Doctor Who Series 10 Episode 11: "World Enough and Time"}

Every indication is that Bill's experiences while waiting for the Doctor have been completely real, with no "embellishing" hallucinations.

As Longspeak remarks in another answer, according to Razor this took place relatively shortly before the Doctor's arrival.