Looking at your pictures I would say the writings on the wall..
I would always agree a price just in case the client thinks it will only take a few hours and get a suprise when he is billed for as long as it takes! No hard feeling then!
Should have tried a section see if it came off easy or hard and how long it took then estimate from there.Just a thought
what r you using james pressure washer or wfp .
You need to TFR that first as well. Unless you have hot in which case use both.If its only half of unit 2 showing Id be thinking along the lines of nothing less than 3 man days. .
Never trust anyone that says "go ahead without a price...i trust you"!