That's a good idea to change into your heels once you're off the boat, so you don't have to limit yourself by that.
I know that feeling, I also always want to be sure that I can walk well enough in my heels before I wear them out. Probably I shouldn't worry too much, but I'm a bit vain when it comes to that 😉
No, actually I never wore any 12 cm heels to the office. The highest ones were 11 cm. 12 cm+ heels are way harder to combine with a outfit, not to stick out as overdressed I think. Also I sometimes have to walk quite a bit over the day. As I said, around 1,5 km sure is the minimum. 12 cm heels would be OK for that, but not as comfortable as something lower. Maybe after I fully managed 13 cm the 12 cm will be so comfortable that I'll wear them to the office as well, we'll see 😉