Hello,
integration period is actually related to signal frequency, cause i supresses frequencies with a period equal to integration period and it's integer mutiples. It has been often used with 100 ms or 20 respectively 16.7 ms period to suppress mains interferences. Cause it needs a time-to-digital converter with sufficient relative solution, it's not suitable for short integration periods.
Has been replaced by SD-converters in most applications in the last years. For high accuracy application, dual-slope linearity is limited by capacitor loss factor.
Regards,
Frank