Technical Writing Checklists: An Overview

Technical Writing Checklists: An Overview

Till v/s Until

Till and until are generally interchangeable in both writing and speech. Till is actually the older word, with until having been formed by the addition to it of the prefix un-, meaning "up to." Till is not the short form of until.
The adjective 'till' is used for qualifying a verb. It does not impose any condition like 'until'.

See the example below:
He waited for her till 5 p.m.
John sleeps till he got a call.
You shouldn't move out until you get my confirmation.

Login v/s Logon

We choose 'log in' for our more technical (vs. consumer) audience, but I agree that going with the standard that your particular users might see (80% makes 'standard') is the way to go.
On the one word vs two word question: English language usage dictates that when used as a verb (action), it's 'log in' or 'logged in'. When used as a noun or adjective (what is your login, or login information) it's one word.