Is it colloquially acceptable to use ETA in place of "estimated time to completion"? [closed]

Literally, ETA means "estimated time to arrival". It is often used when traveling, like you want to know your ETA to your destination, or the ETA for the package delivery.

However, often I find myself wanting to use ETA when I am referring to a completion date, even though literally ETA means arrival, not completion. Obviously, there is no colloquial expression, "ETC", especially since that could be confused with "et cetera" in writing.

I wanted to know what you people think about this, is it colloquially acceptable to use ETA in place of "estimated time to completion"? I do believe the other party would understand, but I am more concerned with proper grammatical usage.

Yes, at least in the hi-tech and software development industry. This phrase/acronym is used for the date of task completion.

See, for example, this forum question:

ETA on fixing the underlying issue

Wikipedia describes this usage:

ETA is also used metaphorically in situations where nothing actually moves physically, as in describing the time estimated for a certain task to complete (e.g. work undertaken by an individual; a computation undertaken by a computer program; or a process undertaken by an organization). The associated term is "estimated time of accomplishment", which may be a backronym.[citation needed] For example, Bittorrent clients specify ETA as the expected time remaining for a file to completely download as 1d4h (1 day and 4 hours), 1w2d (1 week and 2 days), etc.

I personally use and hear it in this way quite a lot, and it's quite common to see in technologic applications in terms of down/uploading files.

A common expression (AmE) for the expected date for completion of a project,delivery of product or a report (and the like) is: "Drop Dead Date".

As in: "I see your company is trying to have the new golf course operational by this spring - what's your Drop Dead Date?"