Is Mt. Silver a post-game location in HGSS?

Question

I read in the site that you can obtain a Larvitar/Pupitar there and I would really love to have one because hey, why not have a Pseudo-Legend right? Tyranitar looks sick too.

I plan on replacing my Quagsire once I got a Tyranitar, though, If it is post-game, then I might consider not getting a Tyranitar and keeping my Quagsire instead. (Main reason of Quagsire is for Earthquake)

Answer 1

The earliest you can get a Larvitar is when the Johto safari zone unlocks, after you've completed the Olivine lighthouse. You'll need to go to the Mountain zone to find it, so there's only a 50% chance that zone will exist in the initial layout; otherwise you'll have to wait until you also unlock the area switcher to force it in. Without blocks (which are unlocked after beating the league), Larvitar will be level 17, and probably have some catching up to do compared to where your team is that at that point, but not as much as a Mt. Silver Larvitar would compared to a typical team at that stage of the game--and importantly, by getting it early, there's still a substantial chunk of the game for it to get that catch-up work in.

Answer 2

Mt. Silver can be reached from Kanto via Route 28 after receiving the sixteen Gym Badges of both Johto and Kanto

So yeah, you need all badges from both regions to get there according to that

Source: https://bulbapedia.bulbagarden.net/wiki/Mt._Silver