I was trying a new tactic - quickly getting to spellhold & underdark, then doing everything in chapter 6 & I go to wondering what sort of time frames people were talking to finish each chapter. It seems Chapter 2 is the typical questing time, although personally I prefer 3 since you have the amulet of power.

So, here's my runs:
Character 2 3 4 5 6 7 End
Jon Mark, human 2 5 19 24 28
L9 Ftr, Mage
Phineas, human 2 21 30 31 37 40
L6 Ftr, Theif
Jonathan, human 2 46 60 64 68 81 87
L9 Ftr, Mage (same BG1 character as Jon Mark)
Constance,human 3
L9 Ftr, Mage
Vicky, 1/2elf 9 18 36
Ftr/Druid (my daughter's run)
Farnham, human 4 8 54 58 63 79 84
L10 Swash, mage
Klindar, elf 3 11 50 54 57 66 68
Ftr/mage/thief [perhaps not representative, as I just got shadowkeeper]
Corwyn, human 3 8
Archer

I have done the majority of quests in the 3rd chapter, usually, and it appears that 80-some days for the whole quest is typical for me.

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WizWom - Wandering Kernel of Happiness

I always try to go to Spellhold as soon as possible. I just want to get Imoen back as quickly as I can since she's one of the most useful NPC's (and she is your sister after all). with Imoen and Nalia (or Edwin) I've got enough magical firepower and don't have to have another thief in the party.
this of course means I do the majority of side-quests in ch.6.
if I do all the quests (except for some NPC specific ones) and with a full party I finish the game in about 50-60 days.