"Pat" wrote

What do I say to this plumber, to be diplomatic yet firm so as not to be
ripped off?

Absolutely nothing. He did not have time to finish the job and will be back
tomorrow. Futhermore, he wasnt 'late' by 45 mins' he was trying to fix
another's problems that took longer than expected. How much later did you
want him to be for the others with frozen pipes? How angry would they be at
2-3 hours delay or told 'sorry, tomorow maybe'?

Think about it. You added even a toilet installation to his list. Your
report rambles a bit but shows lots of extra stuff added at a time
specifically when many suddenly have frozen pipes and may be totally without
water. He reasonably seems to have prioritized.