Hi Sample Rate and Conversion Time are used in different contexts. When we describe oscilloscopes or fast data logger we use sample rate, when we use slow data loggers we use conversion time.
You can think of sample rate being the reciprocal or conversion time. The conversion time of the ADC is the time it takes for the analog signal to be converted to become a digital signal, in devices like the ADC24, TC-08, PT-104 and so on is not very fast (as they do not need to be). So for example the ADC20/24 can take between 60ms to 660ms to convert a signal from analogue to digital (depending on the resolution chosen as this can be varied). So in devices like this we choose to use conversion time, rather than sample rate. If for example you sampled at a rate of 1kS/s (1ms intervals), whilst it is possible to sample at this rate the unit can only change the analogue readings at say 60ms intervals and as such for a period 60ms or 60 samples the data will be identical.
To conclude you can choose to sample at quicker intervals than it takes for the ADC to convert the signal however you readings will remain the same for the conversion time period.
I hope this helps.