If it can no longer pass poop, it will die in a matter of a couple of days. You really need to act as soon as possible.
It is the urates that clog the vent up and prevent the regular poop from passing. Urates are the equivalent of our urine. In birds, the urine passes from the kidneys to the cloaca as a liquid but the body then reabsorbs some of the fluid and the urates are evacuated with regular poop as a white chalky solid, which is the white capping you see on bird poop. If the chick is too hot and becoming dehydrated, the body will reabsorb more water from the urine to conserve it and the urates become more chalky and solid than usual and start to cake the inside of the cloaca until eventually a plug forms and the bird struggles to pass poop or urates and usually it cheeps a lot as it strains to pass waste. Once the digestive system is blocked, toxins build up and food is unable to be processed and the chick will either starve or die of toxic shock