Much like every other aspect of Steampunk, when is a challenge to answer accurately. The reason for this is you first need to define what aspect you are defining the beginning of. First use of a term is a common modern designator for the beginning of a genre; personally, this seems inaccurate, though understandable for non-interested parties. In some genre you see a designation from when someone within the genre and someone unconnected used the descriptor term; this is not necessary in Steampunk. First appearance of solidly representative works is another common time factor. Discussing Steampunk in particular, you see disagreement on this one, not based on difficulty placing writers in the genre but of disagreement when the genre began and what it is. Several 19th century authors are pivotal to Steampunk and for many people define the genre, yet most people say they are precursors and not Steampunk. Several works from the 1950’s and 1960’s are undeniably Steampunk and even reached into mainstream production and popularity. Metropolis from 1927 is a major Steampunk work, often considered, as Wikipedia puts it, “the single most important early film to represent Steampunk as an emerging stylistic genre.”
Given these time references and that representations continue through present, it is interesting that many listings designate Steampunk as having emerged in the 1980’s as a sub-genre of Cyberpunk. First use of the term in a title did not emerge until the 1990’s but that is hardly a key point other than to say it was in common enough use by that point authors were taking advantage of the connections and connotations of the word in a title rather than using the work to show genre. I have trouble with the concept that you need to use a term to fit a genre; it should be obvious on its own. Also, a term usually comes about after a genre is established, simply because there is nothing to describe until it is established. Given this, the genre obviously was in place prior to use of the term, yet even I would be challenged to actually choose a start point for the genre. One point to agree with not beginning the genre in the 19th century is that they were using current and speculative technologies to consider what-if not what many consider outdated or bypassed technologies. Overall, what I see is a distinct and enduring disagreement with no clear answer. If you read my earlier essay about the development of Steampunk and cultures in general, then you will see part of why I find it unlikely a clear and accurate designation of when it began is possible.
on a side note – I missed yesterday due to husband’s birthday and plan an extra project tomorrow to fill, we shall see.