Welcome to the forum.
The RP2040 does not have a lot of analog pins. Therefore the Arduino team made use of the NINA module analog pins. I suspect the pins you have issues with are on the module and you need to get trough an additional interface (hidden from the average user) to make use of the pins therefore the delay.
I recommend you look at the Arduino Nano 33 IoT and Arduino Nano 33 BLE.
They are different from each other. Have a look at their specifications and see what fits your application better. They both make use of their own ADC with enough inputs.