3 stage process, roughly 2 weeks. Explained my earliest start date in the initial interview and there was no issue. Received an offer which I accepted. On a follow up call post offer acceptance I was told that the start date I'd mentioned was no longer good enough despite it being no different to what I said at the start of the process. Their excuse is that it was a replacement hire so they were unable to wait roughly 1 month which is the minimum notice period in many countries... Due to legal implications I was unable to start before that date and because of this they pulled the offer, even though I said I can legally start in 3 weeks as was confirmed by the relevant parties.
Seems that there was no clear understanding between the recruiter and hiring manager and the goal posts kept getting changed. Along with an illegal approach they suggested to get me started sooner. I'd pulled out of other processes for this when accepting so they left me back at square 1. Seeing how they'd handled the situation it's clear I dodged a bullet and would urge others to be cautious.
Final take: Terrible experience, start date was only an issue post offer acceptance. Pointless to lead someone through the process if you can't adhere to the start date they provided in the initial interview. My situation was clearly stated on my CV so super unprofessional from all involved.
Hopefully future candidates are treated with more clarity and don't waste the time of candidates like they did me. Wouldn't recommend, make sure to have other interview processes in place and keep in other processes even after offer acceptance as trust or decency doesn't seem to be a thing here.