Factor - suggest you check the Customer Service standards for UU because there has to be a CS standard agreed with the Regulator (as far as I know).
For Thames Water it is 50 days from the date of customer application if they fail to do the job within that period.
I've recently been through this also and the company have now written to me confirming that the different rate (estimated once actual usage is established for a meter-fitting) will be deemed to have applied from the 50-day deadline. BM