Hi Broomklean,
It is hard to give assistance when there is so little information. Furthermore any price given will be an estimation or a guideline because there are other factors to take into consideration when pricing. I.e. your overheads will not be the same as those offering advice so you can only take the information and adjust it accordingly.
Three Blocks, 16 flats in each. 4 hours I agree seems very long but again with limited information its not clear what works are covered entirely. As asked above whether windows/doors etc is included, whether its hard or soft floors, storage all factors need to be considered. The last thing you want to do is tender for a contract for services and underprice it making it unviable to carryout. Please answer some of the questions asked in order to receive a more acurate guideline for prices.
Look forward to hearing from you.