You have a wrong understanding of the working of this ADC. This delay is given by the time the ADC needs to generate the result of conversion.

The dialog to the ADC should be like this:

1. First, all lines control lines /CS, /WR and /RD must be high.
2. Set /CS low
3. Set /RW low
4. Output the MUX adresses MA0-4 to the ADC
5. Set /RW high again
6. Set /CS high again
7. Write "1" to the port pins transmitting the MUX adresses and receiving the conversion result, to configure them as inputs, to be able to receive data!
8. Now read the /INTR line over and over again and wait for the end of conversion, which is shown you by a low going of /INTR line.
9. If so, set /CS low
10. Set /RD low
11. Read the result of conversion
12. Set /RD high again
13. Set /CS high again

Now the game can repeat again.

Kai Klaas