The delay time to get RPM response after set TACH input bit for MAX31790?

Q:

Customer found MAX31790 will still reply RPM=0 after set the TACH input bit. The delay time is about 2 second before it gets RPM value.
Could you please help to advice what is the delay time to get RPM response after set TACH input bit?
 

A:

It is mentioned in the DS that the fan speed is measured once per second.

And I tested this delay with an EVKIT: connect a 1k pulse/3.3V amplitude/50% duty cycle to TACH1 pin for a tach input

1. Write 0x00 to register 0x02: disable fan1 TACH input;
2. Write 0x88 to register 0x02: enable fan1 TACH input;
3. Wait a delay time
4. Read register 0x18/19: read fan1 TACH

If delay time more than 1s, read OK; if less than 1s( I tried 0.9s) read fail.
This result is matching what DS indicates. So it should wait 1s at least after TACH input bit enable.