Hallo Max,
Maybe the rules are different here in Scotland, but environmental health regulations are very clear on noise limits, even during 'normal' hours. If you exceed the stipulated noise limit, then you can be taken to task over it. Must be a real pain for folk in new-ish flats with poor sound insulation.
I live in a flat with people above and below me. I don't think I would agree with the poster who suggested you play till your neighbours complain. What I did when I moved in was to speak to the people above and below, took them a bottle of wine, introduced myself and at some point said that I play the cello, that I never practice past 9pm but if they ever have issues to let me know. I am pretty sure they can hear me sometimes (I can hear them) but we all live with it.

Good luck!! I didn't take the cello up till I was 44. You have a serious head start!