When can I buy IPO?

Excuse me, I'm interested in investing in an IPO, but I'm not entirely sure when the right time to buy in is. Could you please explain the process and timing of an IPO, and when would be the best moment for me to make my purchase? I've heard that there can be significant gains, but I also want to make sure I'm not jumping in too early or missing out on the best opportunities. Thank you for your help.