Missing something regarding financing

[Brian White]

I must be missing something.  I live in Texas and I'm in the process of buying my first rental property.  I'm applying 25% down on my first property.  After reading so much on BiggerPockets about investing with little or zero down, I'm still confused about how I should be factoring rental cash flow as part of the Debt:Income ratio requirement for mortgage qualification?  How much can be considered and how long before it will be considered, etc?