I was assured that my rent check would arrive between the 20th and the 25th of that month (Rent is due on the 1st, they pay vendors on the 12th, rent checks are mailed around the 20th). 

You have not included any ongoing expenses associated with a rental business/property which is how you arrived at 600 positive instead of 600 negative cash flow. 

So my question is -- what's the typical approach for arriving at a possible purchase value -- as it relates specifically to capturing the NOI in time, especially if it seems to be changing somewhat rapidly?

There are a lot of scary similarities in the market right now as in 05, 06, but agree that the shortage of affordable housing (builders are just now starting to build them, way after the fact) and labor shortage (kids uninterested in the trades) will delay the arrival of a correction (agree it will come eventually).Plus the employment base in Phoenix is much more diverse now than 10-15 years ago (construction & financial) to a lot of technology and corporate support services recently added. 

I think it is almost always better to buy in an up and coming neighborhood than one that has arrived already.

Show your seller how you arrived at your valuation.

Although I am not fully ready to purchase a property (still trying to up my savings), I believe that the time to do so may soon arrive.

How did you arrive at $210 per month cashflow?

It typically arrives in your account 72hours later.  

I’m sure you and your cpa will arrive at the correct answer by tax time.