While I like the idea of this poll, it cannot be properly validated and is also related to personal situations.
For me in the beginning, having $40,000 to invest, buying my first property and have it increase in value by standard 10% in the first year equaled a further $40,000. So it took approximately 1 year to double my money.
If I had never bought any more property with that $40,000 initial cash injection and look back at my per annum gain it looks as follows.
Yr 1/ +100% ($80,000 profit on leveraged investment)
Yr 2/ +200% ($120,00 profit on leveraged investment)
Yr 3/ +300% (160,000 profit on leveraged investment)
Yr 4/ +400% (200,000 profit on leveraged investment)
This is just one investment property, and I used some of MY money to buy it.
What happens if I buy another and didn't use ANY of my money to purchase it???
Huh, well lets see.
Once I had waited 1 year and had doubled my money ($40,000-$80,000) I pull out $40,000 and buy another property.
Yr 1/ 0% gain-$40,000 so back to zero% gain. Haven't lost, nor gained.
Yr 2/ 200% ($80,000 profit on leveraged investments)
Yr 3/ 300% (160,000 profit on leveraged investments)
Yr 4/ 500% (240,000 profit on leveraged investments)
So we see that it depends on net worth (leverage)
It took 1 year to increase my $40,000 by 100% doubling my net worth.
And if I had stopped at two properties, in the 4th year would have increased my starting net worth by 500%
So generally speaking, it takes around 1 year to double your net worth with property.