So if share price is only set one day before trading, I guess you just have that day to decide to buy if you can get allocation from your broker? I'd like to try it but I've never bought an IPO before.
You commit to your broker before, if you're big enough of a player. They'll mostly have allocated to their biggest clients and such.
Pretty hard to get in on a hot IPO, though, as the shares will go to their favorite clients (those with the most money).
I just 'bought' some through ing-diba, you can set a limit.
I have tried a couple of IPOs
You indicate your interest. Also start funding the account. So you fund 7000 for 100 shares at 70. Then they announce the price is 75. You must change the order to fit the funds or have extra money. Of course you can opt out or change the quantity anyways. But I think in both the cases I actually went ahead (Reddit and figma), I had to reconfirm the quantity. You can't be away from the network.