Gerardo -
We cannot specify a maximum time since there isn't data to support a number.
We would recommend that DVDD comes up first to prevent any contention if you are using external reference/clock. The POR reset of the device triggers when both DVDD and AVDD supply conditions have been meet. You would still need to perform the RESET signal as mentioned in the datasheet after the appropriate amount of wait time.
You would also want to make sure that the analog input conditions are not violated if you delay AVDD significantly compared to the analog conditioning circuitry supply.