Worst case scenario can be that all $2^{32}$ host are present on the network each generating $1000$ packets simultaneously in $1$ second.
So, total packet produced in $1$ second $= 2^{32}\times 2^{10}$ $ \text{(assuming 1024 = 1000)}= 2^{42}$
Now, we can distinguish $2^{50}$ packets, after that wrap around (so wrap around time will be when $2^{50}$ identifiers are used)
$2^{42}$ takes $1$ second,
$2^{50}$ will take $=\dfrac{2^{50}}{2^{42}}=2^8=256\text{ seconds.}$