We actually sat down in one of Maths Classes once and worked it out
The shortest number to say is all the single syllable ones
The longest is 777,777...
on average you end up getting about 1.5 numbers a second.
1,000,000/1.5 = 666,666.6*
666,666.6*/60 seconds/60Minutes
=185.185185... hours of pure counting
You can do probably a maximim of 14 hours of counting per day (minimum 8 for sleep and and approx 2 for eating, going to the loo etc)
185.185185.../14 = 13 and a bit days of nothing but counting...
I haven't done Maths for a while, but I think that's the formula we used