Watcher
One of the problems with Twitter as a medium is the lack of space for nuance. There are hundreds of mounts in WoW, and they are obtainable by a wide variety of different means. Some are simple to get, and cheaply bought off vendors; some require great feats of skill like Gladiator and current Mythic raid mounts; some require tremendous luck (e.g. the Elegon mount
星光云端翔龙缰绳); and some require long-term effort (e.g. the
紫色始祖幼龙的缰绳 from
千奇百怪的漫长旅行, or
Darkmoon Faire prizes).
Ultimately they are all cosmetic rewards, and Timewalking is designed to be an evergreen system that we will be expanding over the years. Unlike, say, a Tanaan rep mount that clearly was designed to be earned within the scope of this patch, there will be people doing Timewalking (especially as more dungeons, and more expansions' content get added) throughout the future of WoW, and this represents a long-term goal within that framework.
If you want to rush through dozens of Timewalking dungeons in a short timeframe to be one of the first to get the mount, and you'd find that experience satisfying, then by all means do so. But I certainly wouldn't say that's the intended approach here. The 500-Badge quest turn-in (
漩涡之瓶 or
不稳定的棱镜) is a once-per-event thing (which we definitely could have made clearer), so if you want to take a more measured pace and just do the Timewalking quest each time the event comes around while you happen to otherwise actively be playing, you can get the mount with just a few total hours spent (though over a longer period of real time). It's up to you. In the meantime, there are other items (notably some great alt catch-up gear) available through the system, and those are much more attainably priced.