Offline installer is already available to download from GOG. So faster than 24 hours, which is good. Also an update patch pushed by Larian first is not the same with an offline installer for the entire game. Update patch is way smaller size, that's why it is pushed first, and this is how many games are patched or updated. Though I think that a more plausible reason may be, if Larian provided the full installer together with the patch, that GOG preferred to delay pushing both patch and full offline installer, to not slow bandwidth too much, when numerous BG3 gamers would update it in first hours after release.
