It takes me 4-6 hours for a full run, solo on my ranger. I stick to the custom zones, the extra level from the quests is invaluable, especially at higher levels.
I skip Velks though, because F*CK Velks... seriously that quest needs to be changed to gargoyles (or spiders, even) nothing else in the leveling quests comes close to the difficulty of the Velks dogs, just in the time it takes to run there
Here's what I do:
Level 1-10 - kill the bears in qrg, no need for FoB, not after the first time and you got your pre-nerf Circlet... Just killing the big bear once at level 1 will ding you to level 4
10-20 Paludal, usually returning to qrg 2 times to turn in the quest & get better buffs.
20-40 Mistmoore Mistmoore Mistmoore - if you run (invis) straight to the gargoyles inside the castle at level 20 you'll level once for each one you kill! So 20-30 is about ten kills, return to qrg for the quest, rince repeat until 40, very easy.
40-60 Dulak. You can also go to Fear at 50 if you're bored of Dulak. Head north to the firewall and kill the red-con apes, good xp. AVOID glare lords and tent. terrors as they mass-dispel!
60-65 Can stay in fear if you want, or do BoT, but you can't do the elemental quest until 65. Personally I find 60-65 the hardest, can't use my uber lv 65 gear yet, can't do the BoT quest.. IMO that should be lowered to 60 (and probably the Dulak quest extended to 50 too).
65-70 BoT elementals (and stuff). This is SO easy, with lvl 65 gear/weapons.
I would agree with extending the Dulak quest. I'm on my first play through on my first char right now and I think the Velks quest is much tougher than the others have been. I'm staying in Dulak for now and I'm 55.