Rule of thumb: -ve to +ve cashflow property

Hi

I was wondering if anyone has a rule of thumb or noted from experience how long it takes for a property to go from negative to positive cashflow?

If you assume the rental is 1/100 of the purchase cost on a weekly basis (eg. $300/wk rental on a $300,000 house and land) and interest is about 8%.

Would the doubling cycle of 7-10 years be an appropriate time to take for it to become cashflow positive (allowing also that rents don’t often keep up with capital growth).

Thanks