When should the walimah be held, before or after the akad?

The walimah is held after the marriage contract; its timing is broad, either immediately after the contract or after the couple have consummated the marriage.
Scholars differ on the best time: some Shafi'i scholars hold it is after consummation (dukhul) because of the Prophet's ﷺ practice, while others hold it is immediately after the contract. A feast held before the contract is not technically a walimatul urus, but it is fine as an ordinary meal. In Malaysian practice, the contract is often held a day or a few hours before the feast, and that is permitted. See Walimah.