I think it took me:

1.5 hrs for level 1-10 questing (just the lowbies themselves)
about 4-5 hours for 10-34 (70 mage boosting in instances on one evening) Deadmines -> Stockades -> RFK -> RFD
about 4-5 hours more for 34-48 (70 mage boosting more on the next evening) ZF -- and got 2 x Sul'thraze the Lasher!
then about 2-3 hours to wrap up around 54 (70 mage boosting the last evening) ST
then last levels I quested as it was too much for a 70 mage to boost very efficiently, mostly did Felwood and Un'Goro Crater

That's about 11.5-14.5 hours for a level 70 to boost from 1-54. This was before Lich, around last September. My mage now does at least twice the damage, and could probably boost a little higher than 54 now, if not right to 60. So I guess I can see 8-10 hours being feasible, spending little time looting and just charging through instances, run straight out and reset to do again.