The holy Shaagas Aryeh [in his Turei Even Megilla 29] asked if ביקור of the Korban Pesach may be done when the animal is still chullin or it must be done after the korban is already declared הקדש.
In a shmooze given at a melave malka ten years ago, HaGaon Rav Nosson Geshtetner expressed utter disbelief that the Shaagas Aryeh missed an explicit gemara. In Pesachim [66b] the gemara says that the custom was like Hillel to be מקדיש the animal in the עזרה before שחיטה in order to prevent potential מעילה. It is clear then, that ביקור was done 4 days prior, before the animal was הקדש.
וצע"ג.
