Current Optimized Levelling Time to 110 In 19 Hours /Played (Patreon)

This is my (rough) estimate of the fastest possible levelling time in 7.3.5. It assumes basic heirlooms but no enchants or other special gear.

1-15 Estimated Time 1 hour.

No special techniques other than the use of Fel Meteor, Cracked Radinax and Gunshoes in order to move quickly. Grinding mobs is slightly faster than questing but it makes little difference. Optimal grind locations: Crystal Lake in Elwynn Forest (Alliance Murlocs), Forsaken High Command (Horde, Worgen), Ventura Trading Company (Mulgore). 

15-60 Estimated Time 4 hours.

 Use Method Zero ( https://youtu.be/q0oD3CF3XOk?t=262 ) , use Stockades for Alliance, Ragefire Chasm for Horde. 

60-80 Estimate Time 4 hours.

Method Zero - Hellfire Ramparts. 

80-83 Estimated Time 1 hour.

Alternate Method Zero with Soloing Hellfire Ramparts.

83-85 Estimated Time 1 hour

Lost City Of The Tol'Vir/Temple Of The Jade Serpent. Note this will extend to 90 when Goralyn's method posted below is inevitably fixed.

85-92 Estimated Time 1 hour 30 minutes.

See post by Goralyn here:

https://www.ownedcore.com/forums/world-of-warcraft/world-of-warcraft-exploits/656292-afk-leveling-85-90-well-of-eternity-legion-demon-killing.html

This is a very powerful technique that will likely be gone within days.

92-94 1 hour 30 minutes.

Garrison set-up (use Timeless Isle portal), Treasures and Bonus Objectives. 

94-98 Estimated Time 2 hours.

Shredder vehicle quest exploit: https://www.patreon.com/posts/15048651/

98-110 Estimate Time 3 hours.

Demon Invasions+Bonus Objectives. Use raid reset method to level fast by resetting cooldowns. ( https://www.patreon.com/posts/14460341/ )

Note that if you want to play continuously all this will take longer as you will hit instance cap with Method Zero, and will have to quest when Demon Invasions are not active. 

I have not included class-specific methods in these estimates.