another pokemon heart gold question

so i had this question about the elite four and i have huge trouble leveling up my pokemon. is there ANY way i can get inside Mt. silvr in heart gold without beating the elite four? if not plz tell me a way to level up my pokemon faster. also if you know, could you tell me around how much time it takes to level up my pokemon to lvl 48?

Mt Silver is only accessible after you have all 16 badges.

oh ok. what is a super fast method to lvl up my mons?

There is none really. Just fight the Golbats and Donphans? Idk what the exclusive is in HG cause I have Ursarings in SS and they give amazing exp

oh ok. i will try that