Not sure what you mean by time limit, but the challenge they're facing is to IPO at just the right time to get the highest valuation and keep it up long enough for the private investors to cash out. Things like Anthropic/OpenAI financials leaking put a dent in this plan, as it could tank the valuation, but AFAIK it's all financial black magic mixed with regular guesswork and playing chicken with each other in terms of if/when.