Teeth whitening questions

I’ve just had my first teeth whitening treatment while I’m on holiday in South Korea, and I was wondering how long it normally takes for the colour to settle. I’ll need a crown for my front tooth, which has had a root canal, so I want to make sure the crown matches the final colour of my teeth.

I’m based in the UK, and the price I’ve been quoted here is pretty similar to what I’d pay through the NHS, so I’m considering getting it done while I’m here if I have time. Just wondering how long I should wait after whitening before getting the crown fitted as a second opinion.