Freezing material while it is fresh will help preserve the terpenes. If you are going to wash it (dry or fresh) I would still freeze it 24 hours before washing it. Either way, you want to let it soak in ice water just before you start washing, shorter for fresh frozen, longer for dry material. You want to fully ensure any dry material is fully soaked before agitating as it will more likely break off if it is still dry and contaminate your hash.

If you have the option to freeze fresh or allow to dry, I would always side with freezing fresh.