32 bytes buffer (24 randomly generated bytes by the client + 8 bytes epoch timestamp seconds) encoded to hex:

const nonce = Buffer.alloc(32);
nonce.fill(crypto.randomBytes(24), 0, 24);

const nowEpochSeconds = Math.floor(new Date().getTime() / 1000);
const t = BigInt(nowEpochSeconds);
nonce.writeBigInt64BE(t, 24);